Abstract: With the intensification of the harsh climate and increase of human activities, land use is changing rapidly in the basin scale, and environmental effects caused by land use change is one of the key issues of global change processes. It brought a greater impact on the water environment, and quantitative analysis of the relationship between water pollution and land use is an important basis for land use restructuring. Based data analysis using GIS, with remote sensing image data as an important data source of the SWAT model, through the SWAT modelling water quantity of ChangJiang basin and simulating water quality in 1983 and 2012, the land use space-time change was analyzed, and the relation with the land use of tributary Changjiang basin in Poyang lake basin and the water pollution of the environment was explored. The most sensitive parameters in this SWAT model were crop management parameters, chemical fertilizer parameters and soil parameters. Nitrogen model output was positively related to application rates of fertilizer and soil nitrogen content. In calibration period and validation periods, ammonia nitrogen and total phosphorus was consistent with the measured and simulated values. In calibration period and validation period, ammonia nitrogen relative error evaluation index were 19.67 and 23.89, the correlation coefficient R² of ammonia nitrogen were 0.817 5 and 0.763 2; while total phosphorus evaluation index relative error were 21.95 and 31.33 respectively, the correlation coefficient R² of total phosphorus were 0.838 3 and 0.756 7. The precision of the model met the requirements of the month load simulation. The area of woodland, grassland, water, urban construction land showed an increasing trend, but farmland showed a decreasing trend. Woodland showed the largest proportion of 70%, followed by paddy fields. Paddy contribution to nonpoint source loads of water environment was the greatest, and the basin was slightly more than 20% of the area. The contribution of the total phosphorus to the total amount was 53.48%-57.01%, and 51.86%-51.86% for the total ammonia nitrogen. Dry land per unit area contribution was higher than the forest and urban construction land. It suggests that agricultural non-point source pollution is the main source of agricultural non-point source pollution of water environment. Farming with 25% of the land area, contributed 60%-65% of the nonpoint source pollution load. Therefore, reducing the application of chemical fertilizers and improving the utilization of chemical fertilizers are the most effective way to reduce non-point sources of water environment pollution; while the contribution of forest land for non-point source was the lowest, therefore, converting from farmland to forest will reduce water environmental non-point source pollution. The research results can help to water environment management decisions.

Key words: SWAT, land use, water environment, non-point sources, remote sensing