Abstract: Diamondback moth Plutella xylostella is a worldwide important pest on cruciferous vegetables. Critical thermal maximum (CTMax) is often used as an index for the thermal tolerance of insects. By the method of dynamic heating, this paper measured the CTMax of P. xylostella in a self-assembled device, and studied the effects of development stage, rearing temperature, generation, sex, and heat shock on the thermal tolerance of P. xylostella based on the CTMax values. Reared at 25 ℃, the mean CTMax of the 4th larva  (50.31 ℃) was significantly higher than that of the 1st larva (43.03 ℃), 2nd larva (46.39 ℃), 3rd larva (49.67 ℃), female adult (45.76 ℃), and male adult (47.73 ℃); reared at 20, 25, and 30 ℃, the adults had no significant difference in their CTMax; reared at 30 ℃ for 1-, 3-, and 6 generations, the CTMax of the adults also had no significant difference. In all the treatments, the CTMax of the female and male adults had less difference. Heat shock with 40 ℃ for 45 minutes could make the CTMax of 5 day-old male moth increased from 45.51 ℃ to 46.49 ℃.