Aiming at the cavitation phenomenon which may occurred in the centrifugal pump, caviation test was designed to improve the service performance and operating life of forest fire-extinguishing pump. The test was carried out on the open-type pump cavitation test system, which was mainly composed of AC electrical dynamometer, test-control computer and pump test-bed. The AC electrical dynamometer powered the system, drove the pump to work and transmitted the data to test-control computer for real time reading. And by acquiring all the data at three different working conditions, including the rated working condition, such as the pump flow, speed, the inlet pressure value, the first stage impeller pressure value, the atmospheric pressure value and the experimental temperature, the NPSH and the first stage impeller lift value at the three working conditions were calculated. With NPSH when the first-stage impeller lift value decreased to 3% of no cavitation lift value as the critical one, the critical NPSH discrimination curve at the three working conditions and the NPSH curve of forest fire pump were drawn, then the allowable height of installation was calculated according to the hydraulic loss of the pipeline. It provides guidance for the research and improvement of this type of fire pump's cavitation performance.