Abstract: Using COD as a control index, this paper calculated the monthly environmental capacity and the permited wastewater discharge capacity of wastewater within discharge standards of five rivers in the Tumen River region. The results indicate that the distribution of every month environmental capactity was very uneven, during the two_month abundant-water period, the environmental capacity was about 50% of the year, but during five_month less-water period, the environmental capacity was less than 10% of the year; even judged by wastewater discharge quantity in 1995, during the less-water period, the water quality of the five rivers controlling sections of the mainstream of the Tumen River did not reach the appointed functional water quality standards and there was no environmental capacity to use. Therefore, the river water environmental capacity has become the major restricting factor of exploitation in the Tumen River region, for keeping coordinate development between economic construction and environmental protection in this region, the effective pollution control countermeasures and steps must be taken.