Abstract: The knees have significant meaning to the walking motion and the stability of the biped robot.The focus of the work in this paper is a hybrid model for a passive walker with knees presented with numerical simulation.The dynamics and its characteristics of the biped locomotion have been analyzed.A optimization study on rationality of mass distribution has been done.This paper also presents the rationality of parameter by the model simulation.All the research above has the positive meaning for bridging the gap between existing theoretical models and developing prototype machine.