Due to their great potential for application in the future of photovoltaics, perovskite solar cells (PSCs) have attracted much attention recently. Changing the composition in perovskites is important for improving the performance of PSCs. In this work, PSCs with mixed MA/FA and Br/I components are fabricated. By changing the cation/anion composition, the MA(0.7)FA(0.3)Pb(I0.72Br0.18)(3) PSC shows the negligible I-V hysteresis and the enhanced power conversion efficiency. And the statistics result also shows that devices with proper halide composition have a smaller discreteness in the device performance. We demonstrate that the halide ratio is essential for the formation of high-quality perovskite film with longer radiative carrier recombination lifetime, uniform crystal size, and better surface morphology. It is shown that the halide composition in the mixed PSCs could greatly affect the I-V hysteresis and power conversion efficiency (PCE). A proper Br ratio is important to help the device to alleviate the hysteresis and enhance PCE.