In order to further improve the performance of differential pump, a four blade differential pump driven by noncircular gear with free pitch curve was proposed. The performance calculation model of differential pump driven by noncircular gear with free pitch curve was established. The performance analysis software of differential pump was compiled to analyze the performance of differential pump under different control points, such as displacement, flow and pulsation rate. The results showed that the free pitch curve was better than the optimal Fourier curve. The pitch curve had better local optimization ability, which can effectively improve the maximum modulus of noncircular gear without undercutting and the displacement, reduce the pulsation rate of differential pump, and improve the comprehensive performance of differential pump. Through experimental research, under the same pump size and pipeline environment, the displacement of the differential pump driven by noncircular gear with free pitch curve was increased by 6.6% compared with the optimal Fourier noncircular gear, and the maximum module without undercutting was increased by 18.7%. The bearing capacity of the noncircular gear was effectively improved, and the pulsation rate of the single pump of the differential pump was reduced by 8.3%. It can be seen that the free pitch curve noncircular gear was more conducive to improving the performance of the differential pump.