In order to explore the mechanism of Piriformospora indica to alleviate the phytotoxicity of acetochlor on rape, this article used the mycelium growth rate method and the mycelium suspension culture method to determine the effect of acetochlor on the growth of P.indica,and gas chromatographic mass spectrometry(GC-MS) was also used to detect the residual dynamics of acetochlor in P.indica,the soil to which P.indica was applied,and the rapes that were seed-dressed with P.indica.The results showed that when the mass concentration of acetochlor in the culture medium was 200 mg/L,its relative inhibition rate on the growth rate of P.indica in solid medium was 98.12%,the relative inhibition rates on fresh and dry quality were 95.11% and 96.40% respectively.When the mass concentration of acetochlor was 20,50,100 mg/L,in the suspension culture medium without adding P.indica,the half-life of acetochlor was 115.52 d,after adding different amounts of P.indica cake,the half-life of acetochlor was shortened to less than 9 days.After adding 2 g of P.indica per kg of soil,the half-lives of 50,100 and 200 mg/kg acetochlor in the soil were 10.35,11.18,and 11.55 d,respectively,all lower than the half-life of the treatment without adding P.indica(11.18,11.95,12.38 d).Similarly,the half-life of acetochlor in rape with P.indica was shorter than that in the control group.In summary,the growth of the endophytic fungus P.indica is slowed down by acetochlor,but it can also degrade acetochlor in the medium and accelerate the metabolism of acetochlor in soil and rapes.