Current MEMS design methods do not fulfill the needs of emerging complex MEMS devices. In this paper, a systematic direct solid modeling approach for surface micromachined MEMS design is proposed. In this approach, practical model of a surface micromachined MEMS device, designed in a traditional CAD environment, is simplified firstly; after simplification, masks and process sequences are generated through solid-based mask synthesis; then local variation is used to refining the 3D layer model; finally masks and process sequences are verified in rough simulation and accurate simulation. The approach aims at enabling designers to focus on creative design activity in an intuitive mode.