Abstract: Interaction between avermectin pretreatment and subsequent short-term heat treatment on the 3rd diamondback moth (Plutella xylostella) instar larvae was investigated based on changes in mortality rate, pupation time, pupation rate, eclosion rate and adult emergence rate. When temperatures are set at 35 ℃ or 40 ℃ for 4 h or longer, tested insects exhibit negative effects such as significant increase in mortality rate and decrease in pupation and eclosion rates, adult emergence rate. Compared with 35 ℃, the negative effects at 40 ℃ appear earlier while pupation time delays. 0.56 mg·L^-1 avermectin toxicity significantly improves after 35 ℃ treatment for 12 h. Meanwhile heat tolerant ability of the insects to 35 ℃ treatment for 4 h or 8 h significantly improves by pretreatment with avermectin at 0.14 or 0.56 mg·L^-1. However, avermectin toxicity at 0.14 or 0.56 mg·L^-1 can significantly improve by short-term follow-up heat treatment at 40 ℃ for 2 h or longer. The tolerant ability of the insects to short-term heat treatment at 40 ℃ for 8 h is significantly weakened by pretreatment with avermectin at 0.14 mg·L^-1. 0.56 mg·L^-1 avermectin can weaken insect tolerance to short-term heat treatment at 40 ℃ for 2 h, 4 h or 8 h.