The invention belongs to the technical field of fluid machinery, and particularly relates to a closed test device for the NPSH of a water-filling type submersible pump and a submersible pump for a well. The test device is composed of a cavitation tank, an inlet valve, a non-concentric diffusion tube, a suction tube, a submersible pump, a temperature meter, an inlet pressure gauge, a transition tube, a first seal joint, a revolution speed measurement instrument, an outlet pressure gauge, a water drainage tube, an outlet pressure measurement tube, a second seal joint, a flow meter upstream straight tube segment, an inlet pressure measurement tube, a revolution speed transducer, a flow meter, a flow meter downstream straight tube segment, a flow control valve, a water injection valve, a vacuum pump, a drainage valve, an exhaust tube, a partition plate, a liquid level meter, an extraction valve and a vent valve. The temperature meter, the inlet pressure gauge, the outlet pressure gauge, the revolution speed transducer, the revolution speed measurement instrument and the flow meter are used for measuring key parameters of the NPSH of the submersible pump. The test device has the advantages that the critical NPSH of the submersible pump under the conditions of different flows can be measured through the test device for the NPSH of the submersible pump, and the problem that a cavitation performance test of the submersible pump cannot be carried out is solved.