An experiment was set up to study the effects of five different dosages of straw fast-rot agent treatments （0, 0.1, 0.2, 0.3 and 0.4 g/pot） on rice yield, straw decomposition and soil physicochemical properties under the condition of straw returning field. The results showed that the amount of straw decomposed increased with the increase of the amount of fast-rot agent, and the straw decomposition rate was the largest in the treatment of 0.4 g/pot, which was 13.0%-18.0% higher than that of the treatment without fast-rot agent. Compared with the treatment without fast-rot agent, the yield of the treatment with fast-rot agent was significantly increased by 1.3%-11.1%, and the treatment with 0.2 g/pot performed the best. The yield increased due to higher grains number per panicle and seed setting rate. The application of fast-rot agent could promote the accumulation of dry matter in rice, and the nitrogen accumulation of rice plants at the mature stage increased significantly compared with the treatment without fast-rot agent, and the highest increase was in the treatment of 0.2 g/pot. The application of fast-rot agent could help rice absorb and utilize soil organic matter, total nitrogen content and available nutrients, and improved the level of soil fertilizer supply. The results of this study have reference significance for the efficient utilization of straw resources.