Abstract: Based on the survey data of marine environment in Tianjin coastal waters from 2009 to 2018, this paper systematically analyzed the pollution status, change trend and water quality categories of different environmental parameters. The results show that the seawater quality in the coastal area of Tianjin shows a gradual improvement trend, but the trend is not obvious, and a fundamental improvement trend has not been formed. The main pollutants are nitrogen and phosphorus. Chemical oxygen demand (COD) and petroleum pollution are not obvious, and heavy metals are basically in the concentration range of excellent water quality. Land input is the dominating source of main pollutants in the sea area, but the input of atmospheric precipitation and mariculture could not be ignored. The change of tidal capacity and local hydrodynamic force caused by reclamation project would hinder the transportation of materials in coastal areas, which could lead to the accumulation of pollutants and affect the water quality of local sea areas. It is suggested that while strictly controlling the land-based discharge of nitrogen and phosphorus pollutants into the sea, strengthen the supervision of atmospheric input and aquaculture, and optimize the industrial structure and formulate accurate emission reduction schemes, so as to ensure the harmonious unity of environmental protection and economic and social development in the Bohai Bay under the overall planning of land and sea.