When I bend the legs on animation it looks good but when I play the animation the leg bending is too ugly!! what should I do?
You probably have too many subdivisions, you need large, long, faces to make the animation look good in the game (e.g. they need to stretch) so if they are too small it looks bad.
I just ran into this… try using the W>subdivide_smooth command instead of subsuf when making your model… then you can leave the areas on the knees left with large faces while therest of your body is smooth… Like “selective subsurf” I guess…
SomeBlenderGuy: “I’ve been trying to model a hot car, but when I preview it, it looks UGLY? How come?”
CriticMan: “The problem here is most likely that you suck at modeling.”
We can’t give you a real answer when all you tell us is your product “ugly”. We can only jump to negative assumptions toward your animating/rigging/modeling skills.
I know how to animate the armature! but when I bend the leg it looks good when you’re animating it but when you play it…it doesnt look good! Guys I’m serious! this walking animation is my problem for 1 year!
Seriously!
If you want help post some pictures or a video.
I’m Serious! 
younguser,
Please either post a .blend or show us some pictures of your problem.
“Ugly” could mean anything, so it would help us to know exactly what you don’t like about what it is currently doing. It would be good to see one picture of what looks “good” in the animation, one picture of what looks “ugly” when you play it, and one picture that shows your armature and the model in weight paint mode. Also, show a picture of the mesh topology of your model around the knee area. To get a good knee bending animation you need three edge rings at the knee. If you only have one or two edge rings in the knee area, that could be the culprit.