The invention provides an automatic assembling and clamping device for a cylindrical steel plate. The automatic assembling and clamping device comprises a clamping device base, a fixed support seat, a movable support seat, a front clamping column assembly, a back clamping column, a screw rod and a sliding device, wherein the front clamping column assembly comprises a first front clamping column and a second front clamping column, a screw rod groove is formed in the clamping device base, and the fixed support seat is arranged on one end of the upper end surface of the bottom clamping device base; the first front clamping column and the second front clamping column are vertically arranged on the fixed support seat and rotate around respective center axes, the screw rod is arranged in the screw rod groove of the clamping device base and is driven to rotate around a center axis of the screw rod by an external motor, and the lower end of the movable support seat is in threaded connection with the screw rod; and the back clamping column is vertically arranged on the movable support seat and rotates around a center axis of the back clamping column, and the sliding device is connected with the clamping device base.