Abstract: To evaluate the sustainability of crop rotation system in the cultivated slope land under 17-year continuous chemical fertilization condition in the Loess Hilly Region, in the present study, based on the method of area of triangle, 18 indicators (both soil and crop components) were selected, determined and classified as well as transformed into the three kinds of indexes including the soil physical index, the soil nutrient index and the ground-above crop index. Then, the sustainability index (namely area of triangle) was calculated to assess the status of the crop rotation system with the three indexes according to the triangle method. The results indicated that, there existed an improvement in the system sustainability with the fertilization treatment as compared to the control of N0P0, which did not receive any fertilizer. The determined indexes were all increased in various degrees with the physical index of 19.3 %, nutrient index of 19.6 %, crop index of 200.6 % and the sustainability index of 139.6 %. Along with the increment of single fertilization input (N0P0N1P0\N0P1N2P0\N0P2), the sustainability index increased by 17.7 %, 84.7 % and 76.8 %, 88.9 %, respectively in comparison with the control of N0P0, while far less than the threshold of 1.3 (52.0 %, 26.6 % and 27.8 %, 22.8 %, respectively). Thus, the treatment of single-chemical fertilization was not sustainable in the studied site. However, the treatments of combined with nitrogen and phosphor held a preferable sustainability, in which the sustainability index was averagely 27.4 % more than the critical value (1.3). The rank of the crop rotation system sustainability was N1P2 (1.98) N2P1 (1.74) N2P2 (1.47) N1P1 (1.44). Therefore, the N1P2 (N55.2 kg/ha, P2O5 90 kg/ha) was the optimal chemical fertilizer-applied treatment in the research area.