Abstract: In order to study the hydraulic characteristics, internal flow characteristics and cavitation characteristics of the centrifugal fire pump, numerical analysis was carried out based on the RNG k-ε turbulence model to compare the internal unsteady flow of the centrifugal fire pump with a specific speed of 24.7 under different working conditions. The results show that under the shut-off condition, a lot of stall vortices are generated in the impeller of the centrifugal fire pump, especially the vortex core distribution with large area and extremely high turbulent kinetic energy appears at the outlet of the impeller, which seriously affects the flow passage capacity and causes a lot of energy loss. With the increase of flow rate, the vortex in the channel disappears gradually, the flow field tends to be stable, and the distribution of vortex core basically fixed and symmetrical. With the continuous increase of flow rate, the axial force of centrifugal fire pump increases gradually, and the fluctuation of axial force is relatively strong under the conditions of minimum flow rate and maximum flow rate. With the increase of flow rate, the radial force decreases gradually, and the vector distribution of radial force under different working conditions presents a six tooth distribution. With the increase of flow rate, the influence of cavitation on the head characteristic curve of centrifugal fire pump is more obvious. When the head curve begins to decline, the NPSHR increases gradually, but the decline speed is relatively slow.