A leg mechanism with fixed and centralized drive, no corresponding rotational characteristics at the footand the same movement ability in all directions (OmnilLeg)was reported, in order to improve the performance of OmnilLeg, a multi-objective hierarchical optimization method was proposed to optimize its size parameters. The kinematic model and static model of the leg mechanism was built, six performance evaluation indexes were constructed, including limiting step length, limiting step height, two kinematic performance indexes (mean value of Jacobian matrix condition number, and fluctuation of kinematic performance), and two static performance indexes (ability of force transmission, and stability of force transmission).The influence degree and law of the dimension parameters of the omnidirectional motion bionic leg on the six performance evaluation indexes was analyzed.Combined with Monte Carlo method, a multi-objective dimensional parameter optimization method was proposed to stratify the optimization objectives by taking the ultimate step length and the ultimate step height as the main indexes and the kinematic and static performances as the auxiliary indexes,and the dimensional parameters of the OmnilLeg were optimized.The kinematic properties and static properties of the OmnilLeg were analyzed, and it can be seen that the omnidirectional motion bionic leg possessed better kinematic and hydrostatic performances when the end workspace was in the region of -0.07 m≤(x, y)≤0.07 m, and 5°≤γ≤85°. A prototype of the OmniLeg was built based on the optimized dimensional parameters,a single-legged experimental platform was built, and the conclusions of the kinematic and static properties were verified by end-loading experiments. The research can provide a foundation for further research on the OmnilLeg.