The purpose of this paper is to have a better understanding of the function of human flat foot. To analyze its dynamics, we propose a passive rimless wheel with asymmetric flat feet. The model has a point mass in center and massless spokes. The rigid asymmetric flat feet were equipped at the end of spokes. The walking process of this model which has “heel-strike” and “toe-strike” is similar to human walking which has two peaks of vertical contact force in one stride. The stability was analyzed through eigenvalues of the linearized return map. The energy efficiency was analyzed in two ways, one from CoM trajectory and collision angle, another one from speed and step length. The proposed model has faster walking speed, higher energy efficiency, but lower local stability, compared with regular rimless wheel.