Is it normal?
I've already read many faqs for this Hezrou to find out is there any special strategy to kill him?
There were no special recommendation but my strongest fighter hardly can pass through Hezrou's AC even with bull's strength.

my situation:
1.Water node is the first node that I went to.
2.I can not inflict any damage to iuz too. But i'm glad by chance he summoned into wall and i'm not have to fight with him.
3.I play Atari patch2. My characters has 53700 exp and they are level 10.
4.My strongest fighter has 17 STR, 12 DEX, and equiped hedrack's warr hammer + 2 which inflict 1d12, 20 x3 damage. This fighter can only inflict 5 damage to Hezrou after many many turns.

Any suggestion would be appreciated.

Try using magic.

Also, don't forget that Bull's Strength isn't the only spell that increases accuracy. There's Bless and Enlarge, both of which can affect targets other than the caster.

Also, don't forget that haste also boosts accuracy.

I don't remember if the game lets you "aid another" for another attack bonus at the expense of someone else's action.

Also, don't forget item creation feats, if you have them.

Thank you, I didn't know about it. It help a lot. Now I understand why I can not inflict a lot of damage to him and now I understand better importance of various parameters.

This beast can pass through my AC easily. At this moment the best strategy for me against him is to touch save and load again and again :))

After 45 min fight and touching save and load dozen times I only could inflict 88 damage to him and he is still 'Hurt' :)) I see this dude has more than 400 hp. I'm looking for some opportunity to strengthened my fighter with various potions and scrolls but all I can do in each turn is just to cure him :))

Thank you every one.

Try using all the spells I mentioned above. Remember that bonuses of different types stack. Specifically:

Enlarge gives a size bonus to Strength, which affects accuracy.
Haste gives a haste bonus to hit (and to AC)
Bless gives a morale bonus to hit (so does Aid, if you prefer that spell for some reason). Alternatively, if you have a Bard, you could try inspire courage, which at 8th level should give you a +2 morale bonus (doesn't stack with bless).
Prayer (assuming it's in the game) gives a luck bonus to hit. Note that it also boosts skill checks, so it's useful when doing things like learning spells (assuming the game's implementation is accurate).

One more hint: If you are having trouble hitting, don't use Power Attack; it reduces your accuracy.

Alternatively, if you can only hit on numbers like 19 and 20 anyway, then consider cranking up Power Attack as high as you can go. If you weren't hitting accurately anyway, then you may as well make each 20 count.

The monster has damage reduction 10/holy so if you have holy weapons (they do 2d6 extra damage vs evil creatures) use them. If you have a shield or a second weapon unequip it so you do extra strength damage and +2 damage for each point of power attack. With power attack +10 activated you should do a lot of damage when you hit.
Magic missiles do full damage if they get over SR, summons can soak up damage for you, flanking will grant +2 to hit and allow sneak attacks.

You can travel between the nodes without boss battle, if you explore the others you can find helpful things.

I've found that a Bard's fascinate ability works pretty well to "charm" the node bosses if you have been maxing your perform skill and have high Cha. Especially in late-game when you can craft your own misc magic items to buff your relevant stats to god-like awesomeness.

OR

Just have someone turn invisible and run past the node boss and take the portal back to lvl 4. The rest of the party comes too (kinda lame exploit). You can always come back to finish off the boss when you are freshly equipped/stronger.

Finally I managed to kill hezrou.
What I used:
Bull's strength + Inspire courage + Countersong + Inspire greatness + haste + enlargement + touching save and load until critical hit get confirmed.

Some notes:
1. haste stacks!!! you can cast several haste.
2. Enlargement reduce (-1) from base attack for size adjustment.
3. 10 Power Attack reduce (-10) from base attack and I couldn't find how it can help and I didn't use it at all.
4. Thank you everyone

Power Attack trades attack bonus for damage.
Have a look in the manual (page 46 of the pdf) for an explanation.
It's especially powerful with 2-handed weapons.

First I need to pass through his massive AC. I don't believe its worthy against opponents with high AC.
Base(17) - Powerattack(10) + Roll(20) < AC(30) => Missed

Except that a roll of a 'natural' 20 is always an automatic hit, regardless of AC.

Thanks, didnt know about it.
But how about second roll for critical confirmation? Its 1 in 40 to roll 20 two times.

In D&D 3.5e (the rules ToEE uses) a second 20 will count as a critical confirmation in this case. The probability is 1 in 400 (1/20 x 1/20). I should stress that I'm talking about the D&D rules here, I can't confirm whether ToEE does this but I assume it does.

A critical confirmation is basically a second attack roll. If you "hit" again, you confirm critical. For instance, if you need to roll a 12 or higher to beat their AC and hit them, a roll of 12 or higher will confirm critical. A roll of 20 is not required.

I wanted to throw out my strategy for Herzou's, among other creatures. Mind Fog + Dismissal. Since a Herzou is an Outsider, this is an instant KO! While their spell resistance and will saves can negate this strategy, you still have a decent chance of removing them before having to battle them, especially if you spam both spells. If it all fails, oh well, you were going to end up fighting them anyway. I've had enough success with it that I still use it.