By systematically studying the water system of the Mianyuan River in Tuojiang Valley, the heavy metal pollution conditions in each stream segment of the Mianyuan River were evaluated synthetically. The results showed that the contents of heavy metals comply with the sanitation standard of potable water, and the principal sources of heavy metals in the Mianyuan River are the phosphorous chemical industry, leaching and weathering of phospherate rocks, agricultural fertilizers and so on.