The invention provides a self-balancing flood control water retaining device and method. The device comprises baffles, a vertical column, a pressing plate and reinforcing beams. The vertical column is arranged in the vertical direction of the ground, baffle grooves are welded to the vertical column, and the vertical column is vertically connected with the baffles through the baffle grooves. The pressing plate is arranged in the transverse direction of the ground, the reinforcing beams are welded to the upper surface of the pressing plate, and one end of each reinforcing beam is connected with the vertical column. The pressing plate is tightly attached to the ground, and outward bending moment generated by transverse water pressure at the joints of the vertical column and the reinforcing beams is offset through the joint effect of vertical water pressure, the dead weight of the pressing plate and the dead weights of the reinforcing beams to keep the bending moment of the vertical water pressure and the bending moment of the transverse water pressure to be in self-balancing; meanwhile, outward thrust generated by the transverse water pressure is balanced through friction force between the pressing plate and the ground. Flood can be safely and effectively resisted, labor amount consumption is low, working efficiency is high, when the flood temporarily subsides, detachment is not needed, and the physical consumption of flood fighters is greatly reduced.