In the design of MEMS device, a main problem is to lack the variation method of orienting optimization. By analyzing the manufacturability, this paper proposes a local variation method for 3D geometric model of surface micromachined MEMS devices. Firstly, a concerned face is selected on the 3D geometric model, and a local variation operation is executed in the chosen face. Secondly, the variation operation is mapped automatically and propagated to the 3D geometric model based on manufacturability analysis. Thirdly, a certain mask is determined via variation mapping and propagation of 3D model, and this mask is updated to keep the consistency of the geometrical model and process model. Finally, the experiment results show that the proposed method can effectively achieve the local variation of the 3D geometric model, and promote the efficiency of designer.