The present invention disclosed an algorithm of Cu interconnect dummy inserting, including: divide the surface of semiconductor chip into several square windows with an area of A, each of which is non-overlap; perform a logic operation on each square window; and divide the window into two parts: {circle around (1)} the area to-be-inserted; {circle around (2)} the non-inserting area; determine the metal density of the dummy pattern that should be inserted to each square window and the line width; determine the dummy pattern that should be inserted to the windows according to the metal density, line width, the pre-set dummy pattern and the layouting rules. The beneficial effects of the present invention is: avoided the shortcomings of fill density maximization in the rule-based filling method by using reasonable metal density and line width. And with a combination of the influence of line width and density to the copper plating process and chemical mechanical polishing morphology in model-based filling method, it can achieve a better planarization effect.