The speed of the subzero start-up of proton exchange membrane fuel cells is a hot research topic. However, the cost of the start-up of proton exchange membrane fuel cell is an important factor that affects their commercialization. In this paper, a reused gas cold-start method is developed. Hydrogen air mixture is introduced to the anode of the fuel cell, and the exhausted gas from the anode is introduced to the cathode. Thermal equilibrium at -20 degrees C start-up of the fuel cell is calculated. The best gas ratio is confirmed by the start-up process at -20 degrees C. The fuel consumption and hydrogen utilization of the reused gas cold start and the conventional catalytic reaction cold start are compared. 1/4 is the optimal ration of air/hydrogen. The catalytic reactions take place simultaneously in the anode and the cathode of the fuel cell in there used gas cold-start method, thereby saving energy and time during start up. With this method, the fuel cell can start-up at -40 degrees C, and the performance of the fuel cell does not seem to change after the cold-start process.