Abstract: 【Objective】The purpose of the study was to investigate the effects of equal nitrogen organic substitution on soil and water environment and agronomic effects in rice production,to screen the organic substitution methods suitable for agricultural production in plateau lake basin,and to provide technical support for the prevention and control of agricultural non-point source pollution.【Method】The field experiment of equal nitrogen organic substitution rice planting was carried out in Erhai Lake Basin. The field experiment was conducted to set up four treatments:no fertilizer treatment (CK),equal nitrogen 100% chemical nitrogen fertilizer treatment(CF),equal nitrogen 50% organic fertilizer + 50% chemical nitrogen fertilizer treatment(FM)and equal nitrogen 100% organic fertilizer treatment(CM). Characteristics of dynamic changes of inorganic nitrogen concentration in field surface water and paddy soil during rice growth period and the agronomic effects of rice yield and nitrogen nutrient utilization were systematically analyzed.【Result】The regreening stage of rice(0-7 d after transplanting)was the key risk period to prevent nitrogen loss from field surface water. The peak value of ammonium nitrogen concentrarion in field surface water was FM(20.92 mg/L)> CF(20.07 mg/L)> CM(8.60 mg/L)> CK(6.82 mg/L). The peak value of nitrate nitrogen concentration in field surface water was CM(5.83 mg/L)> CF(3.63 mg/L)> CK(3.14 mg/L)> FM(2.98 mg/L). Compared with CF treatment of single application of chemical fertilizer,total organic substitution of CM treatment reduced the concentration of ammonium nitrogen at the regreening stage of rice in field surface water by 42.23% and increased the concentration of nitrate nitrogen by 134.11%. The booting stage of rice(31-60 d after transplanting)was the key risk period for the leaching loss of nitrate nitrogen in paddy soil. The average content of nitrate nitrogen in paddy soil was CF(11.37 mg/kg)> CM(10.66 mg/kg)> FM(8.71 mg/kg)> CK(7.11 mg/kg). The combined application of organic and inorganic equal nitrogen significantly reduced the content of soil nitrate nitrogen by 23.39% and 18.29% in the FM treatment compared with the CF and CM treatments,respectively. Compared with CF treatment of single application of chemical fertilizer,FM and CM treatments with equal nitrogen organic substitution increased rice grain yield and grain nitrogen uptake by 9.30% and 45.28% in FM treatment and 7.85% and 16.51% in CM treatment,respectively. Equal nitrogen organic substitution(CM and FM treatments)significantly increased rice nitrogen fertilizer contribution rate(31.83% and 37.20% of increase)and nitrogen fertilizer agronomic efficiency(42.22% and 50.00% of increase)(P<0.05).【Conclusion】Equal nitrogen 50% organic fertilizer + 50% chemical nitrogen fertilizer can reduce urea application,stabilize rice production,improve nitrogen fertilizer use efficiency,and reduce the risk of nitrogen loss in paddy fields.