Abstract: The walking supported by three feet of a quadruped walking machine with-pantograph legs is discussed in this paper. The semi-inverse solution is supplied for the kinematic analysis. The kinematic supplementary conditions are determined in advance. D'Alembert's principle and Jourdain's principle are supplied for the dynamic analysis. The difficulty of statical indeterminateness is overcome by introducing the optimum conditions. The dynamic problems of an actual quadruped walking machine are calculated.