Using hybrid rice Yixiang1577 as the material,the mid-season and ratooning hybrid rice yield variation was studied in Southern Sichuan at different levels of nitrogen fertilizer. The results showed that rice yield by using N fertilizer increased to the most signifi cant level than no fertilizer ones,and the mid-season rice and rice yield by using more N fertilizer increased to the signif icant level than less fertilizer ones. The rice yield by using no fertilizer ones increased to the most signif icant level than some used fertilizer,and the ratooning rice and rice yield by using more N fertilizer decreased to the most signifi cant level than less fertilizer ones. The rice yield by using some fertilizer increased to the most signif icant level than no fertilizer ones for mid-season+rationing rice and rice yield by using some fertilizer had no obvious differences at different nitrogen levels. Therefore,application of fertilizer can improve yield of mid-season rice and mid-season+rationing rice. Soil test results showed that nutrient contents in rice fi eld in South Sichuan were very rich in nitrogen,which could provide more adequate crop growth potential soil nitrogen nutrition. The crops with a deep root system had stronger ability of utilization on soil nitrogen. Therefore,the ratooning rice used no or little N fertilizer had a high yield performance because they made full use of soil nitrogen with deep root system. Using hybrid rice Yixiang 1577 as the material, the mid-season and ratooning hybrid rice yield variation was studied in Southern Sichuan at different levels of nitrogen fertilizer. The results said that rice yield by using N fertilizer increased to the most signifi cant level than nitrogen fertilizer. ones, and the mid-season rice and rice yield by using more N fertilizer increased to the signif icant level than less fertilizer ones. The rice yield by using no fertilizer ones increased to the most signif icant level than some used fertilizer, and the ratooning rice and rice yield by using more N fertilizer decreased to the most signifi cant level than less fertilizer ones. The rice yield by using some fertilizer increased to the most signif icant level than no fertilizer ones for mid-season + rationing rice and rice yield by using some fertilizer had no obvious differences at different nitrogen levels. Therefore, application of fertilizer can improve yield of mid-season rice and mid-season + rationi ng rice. Soil test results showed that nutrient contents in rice fi eld in South Sichuan were very rich in nitrogen, which could provide more adequate crop growth potential soil nitrogen nutrition. The crops with a deep root system had stronger ability of utilization on soil nitrogen Therefore, the ratooning rice used no or little N fertilizer had a high yield performance because they make full use of soil nitrogen with deep root system.