I'm using winapi function GetTickCount() with delta time and I'm calculating the displacement of an object on screen like this:

number_Of_Pixels_To_Move_On_Screen = (speed*delta_Time)/number_Of_Pixels_Per_Milllisecond

but I get uneven movement.Sometimes it moves a litle faster ,sometimes slower .
Can someone tell me how to get the object to move at a constant rate?

You need to also limit your frame rate. See this site for a good reference and code.