how can i get GUI.Button presse(or down not click)

Are you talking about "GUI.RepeatButton"? It does the same as button but when you keep the mouse pressed on it

no i want to know mouse down in GUI.Button() (like input.buttondown()) because i want play some effect that timing

sure i can use

 void update()
 {
  if ( buttonRect.contain( input.mousePosition ) )
        DoSomething();
 }

but i thing this code is not intuitive

But thats exactly what you will need to use, rect check + mouse down. Also I think its pretty intuitive, on iOS you work all the time with it as thats how touch works too :)

The GUI.xxx commands only give you a code response (the visual change is automatic) if the action of the element takes place and for buttons thats click