To investigate the effect of the number of teeth on the cavitation characteristics of the cavity at high speed, a simulation model of the flow field with six to nine teeth of the gear pump is created. To study the influence of the number of teeth on the internal cavitation characteristics of the circular arc spiral gear pump and its outlet flow characteristics under high-speed conditions. The results show that the gear pump cavitation characteristics are significantly affected by the number of teeth and the speed; as the number of teeth increases, the extent of the effect of cavitation on the outlet flow decreases significantly. The critical speeds at which the gas volume fraction of the six- to nine-teeth gear pump changes significantly are 9000 RPM, 9000 RPM, 10,000 RPM, and 10,000 RPM, respectively, and after exceeding these critical speeds, the volumetric efficiency begins to decrease while the gas content in the cavity increases abruptly, which seriously affects the continuity and stability of the outlet flow. In addition, when designing gear pumps, increasing the number of teeth helps to inhibit cavitation, improve volumetric efficiency, and reduce pulsating flow.