The optimization of the flow channel structure of proton exchange membrane fuel cell (PEMFC) can improve the mass transfer efficiency of reaction gas and increase the current density, which is an effective method to improve the output performance of PEMFC. First, the geometric model of a single straight channel of PEMFC was established, and the influences of baffle inclinations on the transmission characteristics of reaction gas were studied by adding trapezoidal baffle in the flow channel. The results show that adding baffles in the flow channel can significantly increase the flow rate of reaction gas in the flow channel and promote the mass transmission of reaction gas from the flow channel to the diffusion layer. Increasing the front and rear of inclination angle of the symmetrical and asymmetric trapezoidal baffle can effectively increase the O2 mass fraction under the baffles,  improve the flux of reaction gas in the gas diffusion layer, and strengthen the mass transfer of reactive gases. Compared with the symmetric trapezoidal baffle, the asymmetric trapezoidal baffle with 75° front and 60° back or 60° front and 75° back angles has a better effect on enhancing the mass transfer of the reactant gas. The O2 concentration in the diffusion layer and catalytic layer of PEMFC increases significantly with the increase of the number of baffles, and the peak of reaction gas mole fraction appears in the corresponding area of the baffles. The output performance of PEMFC increases with the number of baffles in the flow channel. The peak power density of PEMFC is 0.435 W/cm2 when 11 asymmetric trapezoidal baffles with 60° front and 75° back inclination are added to the flow channel, which is 6.6% higher than that without baffles. In addition, when the working voltage U=0.1 V, the current density of the flow channel without baffle is 1.57 A/cm2, and when the number of baffles in the flow channel is 11, the current density is 1.80 A/cm2, which increases by about 14.6 %. The research results provide a theoretical basis and technical reserve for the subsequent PEMFC flow field optimization.