One or more life stages of most agricultural pests with short life cycles can be subjected to heat wave stress because of substantially increased frequency and duration of climate change. The ecological effects of heat waves on small insects depend on the thermal tolerance of different life stages. Therefore, analyzing thermal tolerances of insects in their life stages at specific ages is of great significance for understanding the ecological impact of frequent heat waves and climate warming. A worldwide important pest on cruciferous vegetables, diamondback moth Plutella xylostella was used as the test material, the basal thermal tolerance and induced thermal tolerance of 4th larvae and adult were measured, continuous moderate high temperature thermal tolerance of the 1st and 3rd larvae combined with different high temperatures ［(31±1),(33±1),(35±1) ℃］ with exposure time (3,6,9,12 d) were also measured in this study. The results indicated that larvae and adult showed different basal and induced thermal tolerances, larvae with weak basal thermal tolerance showed stronger induced thermal tolerance. Larvae in different life stages showed different survival rates under continuous several days of moderate high temperature stress, larvae have lower survival rate in early life stages than in later life stages. Moreover, this difference is particularly obvious at higher temperatures. The differences of thermal tolerances in different stages of insects have important ecological significance for the maintenance of population. The most agricultural pests have a mixed age structure in their field populations, survival of thermal resistant developmental stage of pests after heat wave will ensure the populations can still survive and reproduce.