Low gas velocity in proton exchange membrane fuel cell (PEMFC) can be occurred as gas distribution inconformity. Low gas velocity of PEMFC aided by gravity water drainage was investigated experimentally. It released that gravity can help droplets separate from gas diffusion layer (GDL) which help the liquid water drainage from PEMFC stack too. The experiment released that the performance of stack will be the best when the cathode downward and the droplet gravity accordance to the orientation of the droplet separate from GDL; Gravity drops consistent with the direction of purge gas in the PEMFC stack when the channel was vertical which improved the water management. In different orientation of PEMFC stack channel the output of stack would be increasing as the temperature rising when the reaction gas flow rate was low. The gas humidification had little effect on stack performance when the channel was vertical. It should be avoided that the cathode was horizontal and upwards when the stack was working.