Abstract: Taking the minimum loss amount of chemical fertilizer as the objective function, and using the planting area, grain demand, economic situation and other aspects as the constraint conditions, the linear programming model was built to get the optimization results of planting structure of Xingyun Lake Basin in 2020 are as follows:(1) The economic crop's largest planting area about 11 069.93 hm², and the fruit tree had the smallest area about 909.40 hm² in 2005-2015. The planting area of gentle slope was much larger than that of steep slope. On the whole, the planting area of rice and dry crop decreased gradually in 2005-2015; the planting area of the economic crop increased gradually; and the planting area of the fruit tree showed a trend that increased at first and then stabilized. (2) After the optimization of the planting structure, the planting area of rice, dry crop, economic crop and fruit tree in Xingyun Lake Basin will be 3 471.56, 2 571.53, 7 966.92 and 2 149 hm², respectively, in 2020. Comparing the situations in 2015, the planting area of rice, dry crop and fruit tree will increase by 1 276.49, 1 051.84 and 1 239.6 hm², respectively, and the planting area of economic crop will decrease by 3 103.01 hm². (3) In 2020, the loss amount of chemical fertilizer after the optimization of planting structure will be 633.79 t, which is 25.47% lower than that in 2015 (890.55 t) in Xingyun Lake Basin. In all kinds of pollutants, the loss amount of total nitrogen decreases most and those of total phosphorus and ammonia nitrogen also decrease, while those of nitrate nitrogen and dissoluble phosphorus increase somewhat.

Key words: non-point source pollution, planting structure, linear programming model