With the development of social economy, water environment capacity has become one key factor that constrains the development of social economy and ecological environment. At present, chemical oxygen demand (COD) and ammonia nitrogen are the main pollutants in the main stream of Songhua River in Jilin City. In this paper, the one-dimensional steady-state model of river was adopted to calculate the water environmental capacity of COD and ammonia nitrogen in the main stream of Songhua River in Jilin city with the method of segment head control. The results showed that the water environmental capacity of COD and ammonia nitrogen in the main stream of Songhua River were 494513.5t/a and 24725.7t/a respectively, the current discharge were 265071.9t/a and 7347.2t/a respectively.  The remaining water environmental capacity of COD and ammonia nitrogen were 229441.6t/a and 17378.4t/a, respectively. At present, the water environmental capacity of COD and ammonia nitrogen in the main stream of Songhua River in Jilin City have a large surplus, which would provide a solid guarantee for the economic development of Jilin City.