The Second Songhua River had undergone a serious,a remissive and a recoverable periods of mercury pollution level during the reseaches (1973-1983).In the serious period,input rates of mercury and methylmereury separately had kept 33kg/day and 1.5kg/day.The level of pollution showed analogy with the Agano River where occurred the second Minamata disease in Japan. In the course of recoverable period,the input rates of mercury and methylmercury sparately had reduced to 0.3kg/day and <3 g/day.So,pollution of water,sediment and fish has been changed into slight and medium levels.Accumulated mercury in sediment amouned to about 50T.It’s to exist as compound with insoluble organic matter and ethiopsite.Deposited mercury entered again into water through scoured and suspened process that maker up about 85 per cent for the total mercury concentration.Mercury of solution transfer mak.ed up <15 per cent.Methylation of mercury is very weak in the sediment.So,concentration of methylmercury is only slightly higher than the environmental background level in the water (0.15ppt).It’s not enough to make methylmercury pollution. Deposited mercury has been outputted by the aquatic environment such as runoff,sanding,irrigation and volatilization et al.The mean output rate of deposited mercury was 0.06.Because output processes of mercury has slow carried under lower concentration conditions,it will not be able to produce new harmfulness on the surroundings.If the pollution source will be strictly controlled,deposited mercury will be purified by the natural purification in the Second Songhua River.