How to modify animation curve in run time?

I have a model. When he play “shooting”, I want to modify animation keyframe to make he’s arm can follow target.How do I do?

You don’t need to modify animation curve for that. Simply change tranform position/rotation values in LateUpdate call, this will override your main animation.

http://unity3d.com/support/resources/example-projects/3rdpersonshooter is a good resource to learn more about animation control.

I do think, you’ll need to have two animations very similar,and try to blend between them at runtime so that your character to follow your target… otherwise to change at runtime an animation clip ,seems rather impossible …