Abstract: Turbidity is one of the most important targets of the water quality of river, higher the turbidity degree, worse the water quality. But in controlling pollution of river water, it may be a good method to control the pollution, even to purify water if use the density reasonablly. Through experiment and investigation on self-purification process and mechansim of water quality in the Songhua River in Harbin, it is found that adsorbent function and coagulative precipitation function of suspended matter play a important part in the river water purification. When the turbidity of river water is between 40 and 400, the Cu and Pb content can be removed 40%-80%, organic matter content can be removed 50%-64%. The main parameters influencing coagulative process according to the theory of orthokinetic Coagulation include effective collision coefficient(α), speed gradient(G) and grain volume density(ô). On the basis of these parameters, the turbidity of river water and the condition of optimal coagulative precipitation of suspended matter is adjusted by draining polluted water to possess different sources. It can get rid of the pollution matter in water even more effectively. This is a economic and effective way in controling water pollution. For controling and teating the water pollution, there are some suggestions:(1) control the exhausts of the pollutant according to total quantity target ;(2) identify the extent of the pollution according to the capacity of the river environment;(3) artificially assist decontamination on the basis of natural water purification.