with magic trackpad, time lag between when i droped a something and when it actually dropped I'm using a magic trackpad.
There is a time lag for about 0.5 second between when i dropped a something, for example desctop icon, and when it actually dropped.

I can drop immidiately by touching after I drop something.
But I don't want to touch every time I drop something.
Magic mouse can drop immidiatelly without any extra operations.

What is this time lag?
And how can I solve this problem?
Do you have one-finger drag enabled? I believe the delay is there so when you "run out of runway" on a long drag, you have time to move your finger to the other side of the pad and continue dragging.  The mouse doesn't need that delay because you can hold the left button (or finger sensor) while you carry the mouse. You may need to use the click-drag instead of one-finger drag.