In order to study the alleviating effect and mechanism of endophytic fungus Piriformospora indica on the phytotoxicity of acetochlor on rape by seed dressing,pot culture experiments were conducted to determine the effect of acetochlor on plant height,fresh weight and root length of rape after seed dressing with Piriformospora indica.The results showed that acetochlor had different degrees of inhibition on the growth of rape when the application rate of active ingredients was 400—2 400 g/ha.The phytotoxic effect of acetochlor on rape could be alleviated to some extent after seed dressing with Piriformospora indica.Among them,when the application amount of acetochlor active ingredients was 400,800,1 200,2 400 g/ha and 1 kg of rapeseed was mixed with 10 g of Piriformospora indica,the recovery rates of plant height were 30.79%,60.99%,26.99% and 26.49%,respectively,the recovery rates of root length were 33.69%,21.51%,58.75% and 31.67%,respectively,and the recovery rates of fresh quality were 75.92%,45.50%,7.25% and 33.33%,respectively.Compared with acetochlor alone,the mass content of GSH and the activities of GST and SOD in the rape seedlings after seed dressing were improved significantly.In summary,Piriformospora indica can increase the activity of related detoxifying enzymes in rape,and enhance the detoxification effect of rape on acetochlor,and reduce the phytotoxicity of acetochlor on rape.