To improve the problem of oil trapping during the operation of external gear pumps, studies on the design of external gear pump teeth and unload groove and the analysis of the effect of their flow characteristics have been carried out. An external gear pump with a new type of unload groove was designed with reference to the general design specification. Based on the computational fluid dynamics (CFD) method, a numerical simulation model of the internal flow field of the gear pump was established, and the simulation analysis of the internal flow characteristics and pressure distribution of the gear pump was carried out to obtain the influence law of unload groove on the performance of the gear pump. The simulation results showed that the unload groove gear pump had a better flow rate, higher capacity efficiency, and less radial pressure than the Default gear pump under the same working conditions and design parameters. The study showed that the external gear pump with unload groove designed in this paper has significantly improved the problems caused by the oil trapping problem compared with the default gear pump.