Metamorphic mechanisms are characterized by variable topology structures,and there exists a great difficulty in the type synthesis of the mechanisms.In this paper,by analyzing the constraint variation features and structure realization patterns of metamorphic joints,a type synthesis method is proposed for the metamorphic mechanism.First,the arithmetic operation of constraint functions is adopted to describe the constraint variation features of the joints in three kinds of metamorphosis processes ( namely,the increase,removal and change of types) . Then, the structure design catalogues of metamorphic joints are established by summarizing and designing the structures of general metamorphic joints.On this basis,a source metamorphic mechanism is constructed by using a morphological matrix,and the metamorphic mechanism types are synthesized by solving the constraint variation features of metamorphic joints and by selecting suitable metamorphic structures.A case study shows that the proposed method can synthesize multiple types of the metamorphic mechanisms satisfying function demand,and it can improve the structure and property of the mechanisms.