The invention discloses a magnet-rheological shock absorber for an automobile suspension system. The magnet-rheological shock absorber comprises a cylinder body, a piston rod, an electromagnetic piston and a floating piston. The shock absorber can realize vibration attenuation by a damping force generated by magnet-rheological liquid flowing through a magnet-rheological liquid channel arranged onthe electromagnetic piston so that the vibration absorption effect can be reached. When in use, the shock absorber can be compensated through the volume change in an air chamber between a base and the floating piston so as to improve the working stability of the shock absorber. The shock absorber has greater loading capacity and can satisfy the operating requirement of heavy vehicles. Besides, through the improvements of the floating piston, the electromagnetic piston, the piston rod sealing structure and the lead structure and the like, the shock absorber can also be improved in working stability, loading capacity and assembling convenience and can be enhanced in the beneficial effects such as the shock absorber stroke and the like.