Abstract: Accurate measurement of the total amount of pollutants into the sea is of great significance to clarify the impact of pollution source emissions on the environmental quality of coastal waters. This study focuses on nitrogen and phosphorus channels into the sea in the land and sea area of Tianjin, and systematically carries out the investigation of pollution sources and the accounting of total amount into the sea. Aiming at the large amount of nitrogen and phosphorus entering the sea in the land area, a set of calculation method of pollutant flux into the sea based on the sea entering coefficient is studied and established. Based on the measured data, the soil loss equation (USLE) model is improved, and the weight coefficient of influencing factors is determined by Delphi method. Finally, a set of coefficient for land nitrogen and phosphorus entering the sea is constructed, based on this system the amount of land nitrgen and phosphorus entering sea can be calculated. Compared with the measured values, this method has high reliability. The survey and estimation results show that during the 13th Five Year Plan period, the average annual input of total nitrogen and total phosphorus in the coastal waters of Tianjin is 14490 tons and 768 tons, in which land nitrogen and phsphorus takes main percentage. The sources of nitrogen and phosphorus pollution in the coastal waters of Tianjin are mainly concentrated in Yongdingxin River, Ji canal, the main stream of Haihe River and Duliujian River, and the pollution is mainly produced by urban residents and livestock and poultry breeding.