Abstract: A case study of Tianjin Coastal Zone in Bohai Bay was performed to research the assessment indicators and assessment method for water environment quality of coastal zones.An absolute grey correlation degree with variable weights was presented,based on the analysis of different computation methods of absolute grey correlation degree widely used at present.The indicator system of coastal water environment was developed,which is composed of physical,chemical and biological indicators.The physical and chemical indicators are made up of COD_Mn,BOD₅,DIN,DIP and DO,etc.,and the biological indicators include the chlorophyll-a concentration and Shannon-Wiener diversity index of phytoplankton,Shannon-Wiener diversity index and Pielou’s evenness index of zooplankton,Shannon-Wiener diversity index and Margalef’s richness index of benthic fauna.Assessment results for Tianjin Coastal Zone indicate that the northern regions,i.e.those nearby Dagukou,are of Class Ⅲ～Ⅳ faced with pollution threatening,the middle and southern regions are of Class Ⅱ,and the offshore sites are of Class Ⅰ with good water quality.These mean that the impairment of coastal water environment quality is mainly suffered by land-based activities.