Abstract: Dalian is one of the most important coastal cities in Northern China and famous for its beautiful scenery and its tourism.As is known,the sea around the city comprises the most noticeable advantages.The protection of the ecological environment of the sea is a necessary premise to the development of the social economy of Dalian.However,in recent years,the increase of the quantity of drainage resulting from the development of its economy has led to the deterioration in the water quality in the near sea.It has formed the major problem of ecological environment in Dalian city.Through researches,this essay not only analyzes the variation of water conditions and the causes,but puts forth some measures to improve it.