The work is a further study on the passive gait biped added with knees, the model can be reduced to a kind of five mass point bar linkage. The further analysis on the variation of the potential energy as well as the kinetical energy has been illustrated, in addition, phase-space limit cycle of a symmetric gait of the robot on a certain degree slope, the conversion law between kinetic energy and potential energy, the energy distribution between the swing leg and stance leg during the walking process have also been presented in detail in the paper, the paper also have a discussion about culmination points which exist in potential and kinetic energy conversion of the coupling two legs. All the research above will have realistic significance in helping us to be better aware of walking rules and global properties of the biped gaits of the robot.