The research was conducted from May to November of 2010, at the demonstrative base of scientific research of hebei academy of agriculture and forestry science in Dehe town of Shijiazhuang city, Hebei province, China. Test was conducted to define of cotton-mung bean intercropping pattern and cotton single pattern, and different N rates (100% N, 5% N off, 15% N off, 30% N off, 100% N off). The objections of this experiment were to evaluate the effects of nitrogen fertilization on dry matter accumulation, number of boll, single boll weight, and seed cotton yield of cotton under cotton-mung bean intercropping pattern as compared to under cotton single pattern. This research was studied in this paper by combination of field experiment and laboratory analysis. The cotton boll results showed that it would significantly affected the number of the total cotton boll if the nitrogen dosage were cut 30%. The differences of single boll weight among all treatments were not significant in this experiment. Under the condition of cotton-mung bean intercropping, the cutting of 15% nitrogen dosage would remarkably affect accumulation of cotton root dry matter in cotton squaring stage. And the cotton-mung bean intercropping pattern was better for accumulating dry matter of the cotton plant than the single cotton pattern in cotton opening stage. The seed cotton yield of cotton-mung bean intercropping pattern was higher than single cotton pattern. The index could provide reference for using reasonable nitrogen fertilization system for the cotton-mung bean intercropping pattern in agriculture.