Human activities have led to serious degradation of lakes in terms of their ecological functions, making the study of the ecological water level of lakes exceedingly important. Based on the current water environment in Bosten Lake, where there is a high concentration of chemical oxygen demand (COD), a study of the ecological water level of Bosten Lake was conducted for water quality management, by analyzing the relationship between COD concentration and water level. Results showed a significant negative correlation between the water level and COD concentration. However, because of the large spatial variation in the COD concentration and multiple influencing factors, the curve estimation between COD concentration and water level was unsatisfactory. To realize water quality management objectives of Bosten Lake with a COD concentration of less than 20 mg/L, the concept of cumulative water level was introduced for statistical analysis to obtain two characteristic water levels:1046.02 m was the average water level for all COD concentrations greater than or equal to 20 mg/L, and it can be used as the minimum ecological water level based on a 60.83% cumulative frequency in the flood season; 1046.4 m was the average water level for all COD concentrations less than or equal to 20 mg/L, and it can be used as the optimal ecological water level based on a 44.70% cumulative frequency in the flood season. The optimal ecological water level of 1046.4 m is consistent with previous studies, which means that it is conducive to both water quality management and overall ecosystem health of Bosten Lake.