Abstract: According to the lunar surface environmental characteristics, a new four variable diameter wheeled lunar rover which consists of a rolling-torsion all wheel steering mechanism was developed. Through the principle analysis of the variable diameter wheel, derived the wheel equivalent radius formula. The calculation formulae based on 3-D environment of positive and inverse kinematics were derived with the method of closed chains coordinates transformation and instantaneous coordinate coincidence founded on the structural characteristic. The kinematic features were analyzed. The theoretical solution and practical solution were deduced. This practical solution can reduce the calculation load. A simplification method of adjusting the pitch angle with the charge of the equivalent radius was suggested. This method can improve the mobility and stability. The results provide the theoretical foundation for structural analysis and motion control of the four-wheeled lunar rover.