A　new　2D　two-phase　flow　model　was　developed　to　study　the　two-phase　mass　transport　in　PEM　fuel　cells　ant　its　effects　on　membrane　resistance　and　cathode　performance.　In　this　model,　catalyst　layers　were　included　in　the　electrodes.　Phase　change　and　its　effects　on　mass　transport　in　the　fuel　cell　were　considered.　The　model　can　be　used　for　both　the　anode　and　the　cathode.　In　this　paper,　two-phase　flow　and　mass　transport　in　the　cathode,　membrane　resistance,　effective　porosity　of　cathode　and　current　density　distribution　were　simulated.　Simulation　results　show　that　increasing　humidification　temperature　decreases　the　membrane　resistance,　but　excessive　humidification　temperature　can　decrease　the　effective　porosity　of　GDL　in　cathode,　and　then　decrease　the　cathode　performance.