[Objectives]  To determine the occurrence of summer diapause and its associated physiological changes in Helicoverpa assulta exposed to high temperature. [Methods]  Summer diapause in H. assulta can be induced by high temperature at different larval stages. In this study, we recorded the diapause rate of H. assulta under 35℃and L16︰D8 beginning at the third, fourth, sixth larval and pupal stage and compared the pupal weight and metabolic rate of diapausing and non-diapausing pupae. [Results]  The summer diapause rates were 25.96%、25.71%、22.76%、11.31%, for third, fourth, sixth, and prepupal stage, respectively. The results show that the diapause rate of the third, fourth and sixth stages was significantly higher than that of the prepupal stage. Furthermore, the summer diapause rates of males were significantly higher than those of females for each tested stage. The pupal weights of diapausing pupae were significantly heavier than those of non-diapausing pupae. We comparatively measured the metabolic levels, using two indices, i.e., body weight loss and respiratory rate, of diapausing and non-diapausing pupae. The weight loss curves of the diapausing pupae were significantly lower than those of the non-diapausing pupae. Moreover, the respiratory rate curve of diapausing pupae was significantly lower than that of non-diapausing pupae. [Conclusion]  The results indicate that diapausing pupae can significantly reduce their metabolism and delay their development under high temperature to survive adverse environmental conditions.