[en] In current effluent discharge standards of the most countries such as Iran, self-purification capacity of rivers have not been considered. These standards developed a similar effluent discharge standard for all of the rivers without considering hydrological and hydraulic conditions of rivers. In this paper in order to show the importance of self-purification capacity and differences between the rivers, in developing effluent discharge standard, two rivers- Gheshlagh River in Kurdistan and Sabzkooh River in Chaharmahal Bakhtiari- as samples were selected., and with applying Qual2kw model, current Iran effluent discharge standards were used to simulate the state of each river. The simulation showed that compliance with this standard maintain an appropriate qualitative condition of Gheshlagh River but in Sabzkoh River, due to the large number of pollution sources, these standards not only does not help to maintain the water quality but will have a very negative impact on water quality. Then Using simulation of river quality, the authorized appropriate limit based on self-purification capacity and the number and type of pollutants were estimated and showed that to develop accurate and efficient standards the self-purification capacity, the number of pollution sources, the amount of waste load and other different conditions of rivers also should be considered.