Porosity　is　the　main　parameter　of　gas　diffusion　layer　and　has　a　great　influence　on　cell　output　performance.　The　electrochemical　reaction　rate　is　various　in　different　region　within　the　cell　and　the　porous　electrode　may　deform　because　of　extrusion　during　assembly.　So　non-uniform　distribution　of　porosity　may　be　more　similar　to　the　real　structure　and　can　change　cell　performance.　Thus,　a　3D,　two-phase　agglomerate　model　is　established　to　explore　the　optimal　three　segments　distributions　of　porosity　both　in　anode　and　cathode　sides　along　three　directions　at　different　voltages　using　the　optimization　algorithm　without　constrains,　and　the　reasons　for　these　results　at　0.2　V,　0.6　V　and　0.8　V　are　also　emphatically　analyzed.　The　results　indicate　that　the　average　of　optimal　porosity　in　three　directions　decreases　with　voltage　increasing.　With　voltage　increasing,　optimal　porosity　increases　from　inlet　to　outlet,　and　the　value　increases　along　width　direction.　When　cell　voltage　is　0.2　V,　the　reaction　rate　is　mainly　determined　by　reactant　content,　but　it　is　influenced　by　charge　transfer　near　inlet　region.　At　0.6　V,　the　rate　is　related　to　charge　transmission,　but　it　is　affected　by　reactant　content　near　outlet　region.