[Objective] To investigate the effects of different straw incorporation methods on soil and water erosion and nitrogen and phosphorus losses in purple soil sloping farmland of southern Sichuan，and to select the optimal straw incorporation method for purple soil sloping farmland in the region. [Methods] Runoff plots were established on a typical purple soil sloping farmland（15°）in southern Sichuan. Five treatments were set up：no straw mulching （CK），low-amount straw mulching（T1：3 744 kg/hm²），high straw mulching（T2：7 488 kg/hm²），low-amount straw mulching+decomposition agent （T3： 3 744 kg/hm²+1.5 kg/hm²）， and high straw mulching+ decomposition agent（T4：7 488 kg/hm²+3 kg/hm²）. Monitoring included rainfall time，rainfall intensity， runoff，sediment characteristics，and nitrogen and phosphorus loss characteristics. The relationships between rainfall， runoff， sediment， and nitrogen and phosphorus losses were analyzed. [Results] 1） Among all treatments，T3 exhibited the best soil and water conservation effect. Compared with CK，it reduced runoff depth （by 40.2%）and sediment loss（by 55.3%）and effectively reduced nitrogen and phosphorus losses. 2）Correlation analysis showed that nitrogen and phosphorus losses were mainly controlled by runoff（p<0.01），but the concentration of total nitrogen （TN） in runoff increased over time， reducing the effectiveness of straw incorporation in controlling nitrogen loss. 3）The TN/TP ratio of runoff in all treatments was less than 22， indicating nitrogen limitation in the runoff of sloping farmland in the region. [Conclusion] Low-amount straw mulching combined with a straw decomposition agent can effectively improve soil and water conservation and nutrient utilization in the purple soil sloping farmland of southern Sichuan， providing a scientific basis for optimizing straw incorporation methods.