oh my god！thanks a lot！I dont even know this “！” mark means that the signal value cant be changed. With your guidance，I achieve my function. I even dont know I could remove this this “！” by a clicking .How stupid I am.Thanks again for saving me.

I just try again，still need a collider.if not，even my sensor and my object are both on the right layer--like the mu layer， my sensor cannot detect this object.  

oh my！thanks ！I thought only when I turn off the “use raycast” property ，I have to add a collider component.