Locks are important safety devices in our daily lives. The purpose of this study is to design new mechanisms of multipoint mortise locks based on a systematic approach. Firstly, the classification and advantages of mechanical locks are introduced, and the definitions and the development of mortise locks are described. Then, the multipoint mortise locks are decomposed into four sub-parts by the different functions, including the latch bolt lock, the dead bolt lock, the dead-latch bolt lock, and the connecting mechanism. The four sub-parts are further analyzed to conclude their structural characteristics as well as design requirements and constraints. Based on Yan's creative mechanism design methodology, the concepts and the atlas of designs are synthesized systematically. One feasible mechanism is further chosen for detail design. Finally, a computer program for simulation is developed and prototypes are built for verifying the design results. The results of this study provide a valuable reference for designing multipoint mortise locks and for the analysis of mechanism characteristics of mortise locks.