Using probability density distribution curve method and aquatic biological criteria, we calculated the water quality target of total nitrogen (TN), total phosphorus(TP), COD_Mn and ammonia nitrogen(NH₃-N) in Erhai Basin based on its history and current ecological data. The water quality targets of TN, TP, COD_Mn and ammonia nitrogen are 0.36, 0.026, 4 and 0.28 mg/L, respectively. According to the water quality target, we got the total maximum daily loads (TMDL) of Lake Erhai. The TMDL were calculated by the linear programming method and the pollutant response coefficient matrix is obtained by MIKE 21 which is the two-dimensional water quality model. MOS (margin of safety) is determined by a first-order error analysis method. After a series of calculations, we got the TMDL plan of Erhai Basin. The results showed that the TMDL of TN, TP, COD_Mn and NH₃-N in Erhai Basin were 2005.989, 149.671, 19258.844 and 1348.119 kg/d, the proportion of MOS were 6.152%,5.570%,4.380% and 5.021%, respectively. The results also showed that agricultural non-point source pollution was the main pollution in the basin and its percent of maximum allowable emissions accounted about 90%.