why Parameter "attack" does not exist?????Thank you!!!

A walk state is changed to attack state

[70080-qq图片20160515090828.png|70080]

This is the script I added to peoplewalk.
[70081-qq图片20160515090840.png|70081]

but i don’t know why Parameter “attack” does not exist?

I think you have the wrong idea. Your STATE is called “attack” but you probably don’t have a PARAMETER called “attack”.
If you want to play a state you have to

anim.Play("attack")

btw, what version are you using