A method for improving the within die uniformity of the metal plug CMP process in the gate last route is provided. Before performing the CMP process for forming the metal plug, a metal etching process is applied, so that the step height between the metal layers in the contact hole area and the non-contact hole area is greatly reduced. Therefore, the relatively small step height will exert a significantly less effect on the following CMP process, so that the step height will be limitedly transferred to the top of metal plug after finishing CMP process. In this way, the recess on top of the metal plug is largely reduced, so that a flat top of the metal plug is obtained, and within die uniformity and electrical properties the device are improved.