The pretreatment (PT) of straw can accelerate the decomposition of the straw. In order to explore the influence of straw returning to the field after different pretreatment on soil nutrients leaching and the amount of COD, the straw was pretreated with white rot fungus, ball mushroom and urea, respectively. The amount of nitrogen, phosphorus and COD leaching out of the soil after straw returning to the field with applying organic fertilizer were studied by the method of indoor artificial soil column simulation. The structure and composition of straw before and after pretreatment were analyzed by scanning electron microscopy (SEM), Fourier infrared spectrum (FTIR), X-ray polycrystal line diffraction (XRD). And the best pretreatment method was determined by comparing the changes of total nitrogen, nitrate nitrogen, ammonium nitrogen, phosphorus, soluble phosphorus and COD of different treatments during the leaching process. The results showed that different methods of straw pretreatment made the straw surface structure changed in different degrees, the intermolecular hydrogen bond aggregation force was weakened, and some carbohydrates were decomposed. Compared with the blank control group (CK), the application of organic fertilizer significantly increased the content of nutrients and COD in the doused solution (p<0.05). In the treatments of involving organic fertilizer, compared with SF1(just organic fertilizer), the leaching amount of total nitrogen in SF2 (pretreated by white-rot fungi and returning, fertilization), SF3 (pretreated by urea and returning, fertilization), SF4 (no pretreatment, returning, fertilization) and SF5 (pretreated by ball cap mushroom, and returning fertilization) decreased by 16.61%, 20.42%, 13.84% and 33.22%, respectively, and the leaching amount of NH₄⁺-N decreased by 4.90%, 22.77%, 18.3% and 38.39%, respectively. Among them, the effect of white-rot fungi on the cumulative leaching loss of total nitrogen and ammonium nitrogen was more significant (p<0.05). There was no significant difference in the leaching loss of NO₃^--N, total phosphorus and dissolved phosphorus among different treatments. Until the end of leaching, the cumulative leaching loss of COD followed the order of SF1 > SF4 > SF3 > SF2 > SF5 > CK. The cumulative leaching loss of COD in SF5 was lower than that in other treatments, which indicated that the straw returning pretreated by the ball cap mushroom could effectively reduce the cumulative leaching loss of COD. In general, the straw pretreated by ball cap mushroom and returning had a positive effect on reducing the leaching loss of soil nitrogen and COD content in the leaching solution.