The invention relates to a stepless damping-force adjustable shock absorber belonging to the technical field of vehicle shock absorption. The stepless damping-force adjustable shock absorber comprises an upper base, a lower base, an upper cylinder cover, a lower cylinder cover, a piston rod, a piston, a working cylinder, an oil storage cylinder and the like. The stepless damping-force adjustable shock absorber is characterized in that the left side of the lower base is provided with a short cylinder, the center of the short cylinder is radially provided with crossed through holes which are communicated with four through holes on a left end surface, and an electro-hydraulic proportional valve and a safety valve are installed in through holes of the lower base; a bent oil channel is arranged on the upper cylinder cover and is provided with two openings, one opening is communicated with a working cavity, and the other opening is communicated with an oil pipe; and the joint of the piston and the piston is provided with a metal raised check ring and a rubber ring. The upper base of the shock absorber is connected with a body of a locomotive, and the lower base is connected with a steering frame. When the locomotive generates shocks, the upper base drives the piston to scretch or compress in the working cylinder to press oil liquid to flow in a system and generate a damping action. Meanwhile, the electro-hydraulic proportional valve controls the size of a tapping area according to the strength of current to control damping force to change along with the working condition of the locomotive so that the damping force can be adjusted and controlled in real time.