Abstract: Under the open-loop condition without external sensing devices,the step-handling walking with relative step height of 10%leg length is realized on a planar bipedal robot Stepper-2D by using virtual slope walking.In order to study the disturbance rejection of virtual slope walking,the ground step disturbance is introduced.Based on the relationship between the pre and post system section states during the step-handling process,it is proved that the step disturbance can be transformed into the perturbation of initial system states and good performance of disturbance rejection of virtual slope walking comes from the stabilizing mechanism of the fixed point.Based on the analysis on the system section states during the transition process,the necessary and sufficient condition for the system to recover from the step disturbance is obtained, further the effect of leg length shorten ratioβ,instantaneous extension angleθ_Ⅱ^* and inter-leg angle(φ)₀ on the maximal relative step height is investigated,and the theoretical explanation for the experimental results of 10%leg length step handling walking is then presented.