A propeller open water test box belongs to the ship assignment technology field and comprises a cover plate, first air cylinders, a box body, a waterproof separation plate, a second box body, a flange, a third box body, a controller, a first motor, a coupling, a support frame, a rotating shaft, a large gear, a transmission shaft, a sleeve, a first slide rail, a first slide block, a small gear, a second motor, a second bolt, a clamping plate, a double end air cylinder, a support, a second slide block, a first bolt and a second slide rail. A lower end of the first box body is installed in the second box body. The waterproof separation plate is installed between the first box body and the second box body. The cover plate is installed on the first box body. Left and right sides, which are below the cover plate, are provided with the first air cylinders respectively. Piston rods of the first air cylinders are connected to the second box body. The second box body is installed on the flange. The flange is installed on the third box body. The test box has an advantage that a clamping device is arranged.