The dynamic modeling and analysis of a new kind of bionic robot which had the characteristics of large capacity，fast walking and good lateral decoupling was carried out. Firstly, the layout of the leg mechanism was introduced, the kinematics analysis was carried out, the explicit linear velocity Jacobi was established, and the explicit expressions of each component’s velocity and terminal linear velocity were derived, which laid a foundation for dynamic modeling. Then, the explicit dynamic equation of leg mechanism was established by using Lagrange equation, and the inverse dynamics of leg mechanism was deduced. Finally, the inverse dynamics equation of the leg mechanism was verified by an example, and the effect of the asynchronous length on the maximum output force of the hydraulic cylinder was analyzed. The moving energy consumption of bionic robot was analyzed according to the inverse dynamic equation. An example showed that the theoretical derivation of dynamic equation was correct. At the moment when the feet landed on the ground, each drive hydraulic cylinder produced the maximum output force, which was independent of the lift height of the leg. When walking in straight and lateral direction, the output force of hydraulic cylinder was increased monotonously with the increase of step length. When walking in the lateral direction of leg mechanism, the maximum output force of the three driving cylinders was lateral swing cylinder, which laid a foundation for the design of buffer structure and dynamic parameters. By analyzing the influence of different gait parameters on energy consumption index of the whole machine, the method of reducing energy consumption was summarized, which provided basis for the gait parameter optimization and trajectory planning of the quadruped robot.