The present invention provides a method for optimizing metal planarization process, comprising: removing a bulk metal layer on a top surface of an interconnection structure by a stressed polishing process until the thickness of the remained metal layer reaches a predetermined value Y, the remained metal layer being a continuous layer covering the top surface of the interconnection structure, wherein the remained metal layer has a first surface mean roughness Ra1 induced by the stressed polishing process; removing the remained metal layer on the top surface of the interconnection structure by a stress free polishing process, the top surface of the metal layer in recessed areas in the interconnection structure being lower than the top surface of the interconnection structure by a dishing value H2 after the stress free polishing process, wherein the metal layer in the recessed areas has a second surface mean roughness Ra2 induced by the stress free polishing process, dividing the removing thickness of the stress free polishing process by Ra2 for obtaining a ratio a; wherein when setting a dishing value, for obtaining the minimum metal surface roughness after the stress free polishing process, the thickness of the remained metal layer after the stressed polishing process satisfies the following equation: Y= α/6 *H2-αRa1.