Abstract: The physico-chemical characteristics and seasonal changes of different waters in Heilongjiang system were studied from May to September, 2001. The results are as follows. Heilongjiang system has good water quality, tansparency mean 41cm, pH value 7. 45, dissolved oxygen was rich, and the water type belongs to CCa I and soft water. The contents of major nutrient elements were high, the content of TN in water was 0. 483mg#L- 1, and the content of phosphate was lower. There were hydrobgial and seasonal changes of the physico-chemical characteristics of different waters, but changes did not occur markedly. The water quality changes of different seasons and major physico-chemical factors, nutrient state and the correlation were discussed and assessed. This study provides a theoretical basis for fishery and sustainable use of f ishery resources.