In order to study the influence of channel size on the performance of proton exchange membrane fuel cell (FEMFC), A three-dimensional model of proton exchange membrane fuel cell was established by COMSOL. The influence on fuel cell performance was analyzed when the ratio of channel width to ridge width is 1:1, 1:2 and 1:3, respectively, and the validity and reliability of the model was verified. Further study shows that when the ridge width remains unchanged, the ratio of the channel width to the ridge width is 1:1, 2:1, and 3:1, respectively. The influences of current density, hydrogen concentration at anode and oxygen concentration at cathode were analyzed. It is found that which is the best size ratio of fuel cell of channel width to ridge width is 1:1, and the ridge width has more influence on the fuel cell performance than the channel width.