The total pollutant load assessment is the key of water quality protection and total quantity control policy. Due to complicated mechanism of non-point pollution, there is lack of the effective methods to assess the non-point pollutant load, and the total pollutant load assessment are limited. This paper, aim at the eutrophication problem of Taihu lake, selects the sub-watersheds in Xitiaoxi watershed and nearby region with one landuse type mainly, analyze the relationship between landuse type and runoff concentration, and assess the nutrient pollutant load. Then, the point pollutant load is assess by the social-economic data and pollutant output rate of different industry type and living water. Based on the assessment of point and non-point pollutant load, the total nutrient pollutant and decay rate are calculated. According to the result of this study, the total nitrogen and phosphorus concentration of runoff from forest land are 0.715mg/l and 0.039mg/l, from agriculture land 2.092mg/l and 0.166mg/l, respectively. The total nitrogen load are 3143.43t/a in Xitiaoxi watershed, non-point nitrogen load is 1589.52t/a. The total phosphorus load are 226.32t/a and non-point phosphorus load is 108.36t/a. In Xitiaoxi river system, the annual decay rate of river network to total nitrogen load and phosphorus are 35.39% and 21.48%, respectively.