Abstract: In order to optimal design for the statics of the six-legged robot's parallel mechanical leg, a statics optimal design method based on the mapping of both constraint and actuation forces was proposed. Firstly, the mapping of both constraint and actuation was analyzed, and the constraint and actuation Jacobian matrix was established. Then, based on the actuation Jacobian matrix, the actuation statics transmission equation was established, the performance evaluation index of actuation statics was designed, and the relationship between the performance evaluation index and structure parameters was analyzed. Through the same way, the constraint the statics analysis was conducted. Finally, based on the performance evaluation index both of constraint and actuation statics, the structure parameters were optimal designed by Monte Carlo method. Calculations showed that when the parameter of the fixed platform was 200 mm, the parameter of the connecting rod was 70 mm, the parameter of the motion platform was 50 mm, the minimum rod length of branch No.1 and 3 was 530 mm, the minimum rod length of branch 2 was 330 mm, the maximum rod length of branch No.1 and 3 was 900 mm, the maximum rod length of branch No.2 was 600 mm, the statics performance of the mechanical leg was the best. The studies laid the theoretical foundation for further study of the six-legged robot.