By measuring photoluminescence spectra of each point along the slope of several polished GaP:N green light emitting liquid phase epitary (LPE) slices,the photoluminescence intensities of p- and n-type crystals are compared,it is found when nitrogen concentration is equal on two sides of p-n junction approximately,the main luminescence region is p-type region,though there is also light emitting from n-type region.The photoluminescence intensities in the former region are about 3 to 5 times of that in the latter region.