I have 2 questions:
1.I'm monarchy,no war weariness,but now after more new cities captured I have main cities with unhappiness,need entertainers .In Civ III is too like in Civ II,unhappiness due to civilization size?
Yes, there is unhappiness due to town size/ difficulty level: the number of citizens born content by default decreases from 5 (at Warlord difficulty) to 1 (at Emperor and above). Captured cities may also have unhappiness due to Despotic/ Feudal(?)/ Communist/ Fascist whip-rushing by the ruthless AI, and/or conscription (in towns >Pop6), and/or foreign nationals being unhappy at your war against their motherland (which is not the same as war-weariness).
Also, bear in mind that Whipping (possibly also Conscription?)-unhappiness doesn't go away when a town changes hands, and cannot be solved by abandoning a captured town: that unhappiness is then transferred to the town's nearest neighbour(s). So you can easily end up with Whip-unhappiness in towns which were never whipped by you.
You can find out why there is unhappiness in any given city, by clicking on one of the unhappy-citizen popheads in the city-screen:
"It's just too crowded" = Overpopulation
"All we are sayin'..." = War weariness (so you won't see this one under Despotism/ Monarchy/ Communism/ Fascism)
"Stop the aggression...!" = Foreign citizen unhappiness
"We cannot forget the cruel oppression..." = Whipping
"No more draft! Hell, no..." = Conscription
2.How can see my casualties,units lost,I don't see this option in the game? In CivAssist too,I don't see this.
This information is not provided by the game. The closest thing is the F3 (military advisor) screen, which shows 'Units lost to/captured from' at the bottom of your current unit-inventory, but this only applies to the capture-able units, i.e. (in the base game) Workers, bombardment-units (Catapults, etc.), and Scouts (if EXP).