There is no lo pan in sF

[mari]

Or he is in the ring, enyway, i cannot chalange him.is there eny way to fix this bug?

 

[Darek]

From The Nearly Ultimate Fallout 2 Guide:

The first time you come here, if you walk towards the village square you'll see two people in a fighting ring, who exchange a few blows and then disappear. Those are the martial arts dudes of this town. Beware that once you've triggered the scripted sequence, you mustn't leave the map before they've left the ring (this is possible if you run towards the exit as soon as they begin), or Lo Pan will be stuck inside.

You didn't give much info, but I'm guessing that's your problem.
If so, what you can do is:
First leave San Fransisco, save your game. Then exit Fallout, copy the file SFCHINA.SAV from a working save slot (one where you have been to San Francisco) into your broken save slot. In case you don't have that, start your game, push Ctrl-R at the title screen, load up the SFChina.map and save game to any available slot and get the file from there.