Gas　diffusion　layer　and　catalyst　layer　are　the　main　components　in　a　proton　exchange　membrane　fuel　cell.　Gas　diffusion　layer　porosity,　platinum,　carbon　and　ionomer　inside　catalyst　layer　are　also　the　kay　parameters　in　these　two　porous　layer,　the　values　have　a　great　effect　on　cell　output　performance.　Considering　the　correlation　between　mass　transfer　and　electrochemical　reaction　rate,　there　is　a　strong　interaction　among　these　four　parameters.　Thus,　a　3D　agglomerate　model　is　established　to　analyze　the　effect　mechanism　of　these　four　parameters　on　cell　per-formance　from　mass　transfer.　Then,　these　parameters　are　optimized　simultaneously.　The　results　show　that　more　oxygen　on　the　surface　of　platinum　improves　electrochemical　reaction　rate.　Cell　performance　can　be　improved　with　platinum　or　carbon　loading　increasing,　while　higher　porosity　or　less　ionomer　can　improve　cell　performance　at　high　current　density.　More　platinum　or　carbon,　or　lower　ionomer　content　all　reduces　oxygen　transfer　resis-tance.　Activation　and　concentration　loss　reduce　obviously　under　higher　porosity　or　more　carbon.　Higher　per-formance　corresponds　to　stronger　bidirectional　mass　transfer　at　the　interface　between　gas　diffusion　layer　and　catalyst　layer　of　cathode　side.　The　current　density　of　the　cell　with　optimized　parameters　can　be　improved　at　least　9.1%.