Impinging stream reactor were used in various applications including pharmaceuticals, petroleum and provisions due to their high mass transfer efficiency, especially in fluid mixing processes, and the difference in structure was a key factor affecting the mixing effect of the reactor, thus optimizing the structure of the impinging stream reactor was beneficial for its further industrial applications. In this work, numerical simulations were used to analyze the internal flow field of a multi-nozzle symmetric impinging stream reactor to optimize the reactor structure. The effects of different nozzle numbers and feed conditions on the velocity field and turbulence characteristics in the impinging stream reactor were investigated, and the mixing effect was characterized by the mixing uniformity. The results showed that the velocity distribution in the impinging stream reactor with different number of nozzles was bimodal, the velocity gradient decreased with the increase of the number of nozzles under the condition of equal velocity, and the distribution range of high shear force increased and then decreased with the increase of the number of nozzles. By analyzing the turbulence scale distribution, it was found that the small-scale vortices were mainly concentrated in the impingement zone, while the large-scale vortices were mainly concentrated in the development zone, and the average shear stress and vortex size gradient in the four-nozzle impinging stream reactor were the largest, and the high shear stress and vortex size gradient were beneficial to increase the fluid turbulence intensity, so the average turbulent kinetic energy in the impinging stream reactor was increased and then decreased with the increase of the nozzle number, in which the average turbulent energy in the four-nozzle impact reactor was the largest, and the four-nozzle structure was more conducive to enhanced mixing. In this study, the four-nozzle structure was the optimal structure for mixing in the impinging stream reactor.