Subzero　start-up　of　the　polymer　electrolyte　membrane　fuel　cell　(PEMFC)　is　one　of　the　most　challenging　tasks　to　be　solved　before　commercialization.　During　the　subzero　start-up　process,　water　generated　in　the　oxygen　reduction　reaction　at　the　cathode　side　of　PEMFC　is　susceptible　to　freeze?which　makes　active　sites　covered　by　the　ice　and　gases　failed　to　reach　the　surface　of　the　catalyst　layer　(CL),　leading　to　a　substantial　decay　and　even　ending　up　with　a　failure　of　the　start-up.　Given　that　many　factors　affect　the　cold　start　process,　the　relative　contribution　of　the　essential　factors　on　the　cold　start　process　is　independently　analyzed　using　first-order　finite-difference　sensitivity　analysis　from　-20　degrees　C　to　-30　degrees　C.　The　effect　of　essential　parameters　on　the　cold　start　process　is　quantified.　The　investigated　parameters　include　the　ratio　of　bipolar　plate　(BP)　thickness　to　that　of　the　CL　(R-BP/CL),　the　starting　voltage　(V-ini),　stoichiometry　ratios,　inlet　gas　temperature　(T-in),　the　porosity　of　the　CL　(epsilon(CL)),　initial　membrane　water　content　(lambda(ini)),　membrane　thickness　(theta(mem)),　the　volume　fraction　of　ionomer　(omega(CL))　in　CLs,　and　the　heat　capacity　of　the　BP　(rho　c(pBP)).　Results　show　that　the　cold　start　process　is　most　sensitive　to　R-BP/CL　and　lambda(ini).　Significant　improvement　of　cold　start　performance　can　be　achieved　by　appropriately　adjusting　R-BP/CL,　lambda(ini),　T-in,　and　epsilon(CL).　Appropriately　increasing　the　V-ini　also　can　be　a　method　to　improve　cold　start　performance,　especially　for　the　cold　start　from　-30　degrees　C.　Besides,　optimized　omega(CL)　in　CLs,　proper　theta(mem),　and　lower　rho　c(pBP)　can　contribute　to　better　performance,　especially　for　the　cold　start　from　-20　degrees　C.