In order to improve the local space utilization, this paper researches on simplify method for irregular objects. Simplify method based on multi-granularity is proposed. According to the collision possibility of each object in the initial layout, different granularities are set for different objects. For one object, its global threshold and local threshold can be calculated by granularity. The object mode is determined by the relationship between Vchobj-Vobj and global threshold and the relationship between Vsubmax and local threshold. The object modes include prototype, convex hull and simplified analogue that own some special geometry features. Approaches for special Boolean blocks are set. A system was developed to verity the feasibility of the proposed method. Compared to single granularity simplify method, simplify method based on multi-granularity can improve the layout compactness effectively.