A three-leg asteroid lander was designed, its structure and working principle, introduced and the physical and dynamic model of the lander established. The electromagnetic damping buffer was used in accordance with the dynamic braking theory to deduce a soft landing of the lander. Meanwhile, the resistance chopper control method was proposed to achieve the adjustment and optimization of electromagnetic damping coefficient and to, solve the problem of small damping force of the buffer at low speed. The semi-active control method and the passive control method were sinulated with Matlab/Simulink,It is concluded that the semi-active control has a smooth power dissipation curve, and the rebound velocity of the lander is reduced by 71.6%.