Abstract: In this paper, a factor diagnostic model based on the method of factor analysis was constructed to study the major pollution factors and spatial distribution characteristics in Dalian bay, and the contribution rate of different types of discharge sources to adjacent waters were diagnosed through the analysis of odds ratio of different sites in local bay and sewage discharging characteristics of different polloution sources.The results of factor diagnosis showed that 5 main pollution modes were existed in Dalian bay, especially industrial wastewater, sewage and Machining Wastewater. The ratio study of different pollutant sources in Choushui tao area indicated that industrial wastewater, sewage and Machining Wastewater had a larger contribution rate with the maximum percentage of 24.7%, 44.1% and 40.1%, respectively.