The invention discloses a mucus drag reduction device for a underwater vehicle, which belongs to the technical field of ship drag reduction and efficiency increasing. The mucus drag reduction device for the underwater vehicle comprises an air cylinder, a piston cylinder, a flow control valve, a controller, a joint, mucus, an air pipe and liquid pipes. The cavity of the piston cylinder is divided into two parts through a piston; the cavity on one side is connected with the air cylinder through the air pipe; the mucus is within the cavity on the other side; the cavity, full of the mucus, of the piston cylinder is connected with an inlet of the joint through the liquid pipe with the flow control valve; more than one outlets of the joint are respectively connected with mucus releasing holes in a underwater vehicle housing through the liquid pipes; and the controller is connected with the flow control valve. According to the invention, the drag reducing mucus releasing speed can be automatically adjusted according to the navigational speed of the underwater vehicle so that the drag reducing mucus uniformly and persistently cover most external surface of the underwater vehicle to increase the maximum navigational speed of the underwater vehicle and energy consumption can be also reduced at equivalent navigational speed.