Abstract: To solve the complex and couple problem of the hybrid mechanism,an equivalent method of generalized-kinematic-chain was put forward to obtain the mobility. Based on the screw theory,the constraint and mobility of a dendriform-hybrid mechanism was analyzed using the method of generalizedkinematic-chain replacement,and the complicated mechanism was transferred into a simply mechanism,thus the correct mobility was obtained. Result shows that the method can effectively simplify the structure of a hybrid mechanism,and provides a certain theoretical basis for further analysis of complex coupled mechanisms.