For a better understanding of the essential characteristics of passive robot,making the research of model be a better guide to the design of actual prototype,methods of numerical simulation and verification of Adams were employed to research a two-dimensional pure passive walking model with round feet.Characteristics of the passive model were analyzed and the dynamic equations were derived with Lagrange Equation. Based on the phenomenon of dynamics of symmetric gait of the robot appearing to be a limit cycle in the phase space,a complete process of the simulation of steady-walking of this model was given with Matlab tool and the initial conditions of the steady-walking model were achieved.The dynamics and characteristics in each stage of the biped locomotion cycle were discussed.Adams was used to verify the simulation.This study will be the basis of stability analysis of the robot and a guide to the design of a passive robot prototype.