The invention relates to a mechanical artificial anal sphincter device capable of realizing constant-force clamping, which comprises an upper fixed top plate, a lower fixed bottom plate, a pair of transmission guide rods, a clamping mechanism, a constant-force mechanism and a transmission mechanism, a pair of transmission guide rods is vertically arranged between the upper fixing top plate and the lower fixing bottom plate at intervals, the clamping mechanism comprises an upper gripper and a lower gripper which are arranged up and down respectively, a channel which is used for containing intestinal canals and is adjustable in size is formed between the upper gripper and the lower gripper, and the constant force mechanism comprises an upper push plate, a lower push plate and paired shape memory alloy plates. The upper push plate and the lower push plate are movably arranged on the transmission guide rod up and down in the length direction of the transmission guide rod, the upper gripper is fixed to the bottom of the lower push plate, and the transmission mechanism is in transmission connection with the upper push plate. Compared with the prior art, constant-force clamping of the intestinal canal tissue by the clamping mechanism is achieved, and the problem of avascular necrosis of the intestinal canal tissue caused by mechanical mismatching of sphincter and the intestinal canal tissue is solved.