get/return the touched object name when i touch on the screen

Can you show us how you are using the raycast? It should work.

   Touch touch = Input.touches[0];
   Ray touchRay = cam.ScreenPointToRay(touch.position);
 
   foreach( RaycastHit hit in Physics.RaycastAll(touchRay) ) {
 
   print("touching object name="+hit.transform.name);
                  
                  }

here is partial code. thanks for your help.

What kind of problem do you have ? Does it log something in console ?

Anyway, try that code :

         void Update()
         {
             if ( Input.touchCount != 0 )
             {
                 Touch touch = Input.touches[0];
                 Ray ray = Camera.mainCamera.ScreenPointToRay(touch.position);
                 RaycastHit hit;
                 
                 if ( Physics.Raycast(ray, out hit, 100f ) )
                 {
                     Debug.Log(hit.transform.gameObject.name);
                 }
             }
         }

in fact, i write the code "print(hit.transform.gameObject.name);"and nothing print out.
$$anonymous$$y project is a map using gesture work. i put these code in Drag function, i want to realize when my finger on the screen,there is a function can return the name of object which i am touching on. Do you have any good idea?

I didn't know there was a print(). But I guess if you've been using it so far, it must work well. :)

Looking at your code, it's quite possible that your Raycast does not hit anything and thus foreach statement is never entered. Try to specify a distance in your RaycastAll function (though that shouldn't be it, since default is infinity) :

 Physics.RaycastAll ( ray, 100f );

BTW, you should also check that your objects are not on the IgnoreRaycast layer. Also, try to draw your ray like this and see if it hit anything in your scene :

 Debug.DrawLine( ray.origin, ray.origin+ray.direction*100f );