The invention provides a ducted propeller with equal forward and reverse thrust force. According to the ducted propeller, on the condition that the rotating speed is constant, thrust force same in magnitude and opposite in direction can be generated when a screw propeller rotates forwardly and reversely, and the propulsive efficiency is high. In order to guarantee that the same inflow condition is provided for forward rotation and reverse rotation of the screw propeller, a fairing with the airfoil profile that the outside of the fairing is flat, the inside of the fairing is convex, and the axial section is symmetric front and back is designed. In order to guarantee that the thrust force is equal when the screw propeller rotates forwardly and reversely, special design is conducted for propeller blades, fusiform sections are adopted for radius profiles, fan-shaped blades are free of side or longitudinal inclination and are provided with wide blade tips, and the whole screw propeller is arranged in the middle of the fairing. A propeller hub, a hub cap and a cabin are equal in diameter and streamlined in shape, and the end of the hub cap and the end of the cabin have the same shape. The ducted propeller with the equal forward and reverse thrust force is simple in structure, easy to realize, and capable of greatly facilitating improvement of the maneuvering property of an underwater robot.