Abstract: In order to understand the effects of fluctuating thermal regime (FTR) on the cold tolerance of female and male Aphidius gifuensis adults in the mummies of Schizaphis graminum and to explore the variation patterns of the biochemical substances in the adult body, this paper determined the supercooling point (SCP), freezing point (FP), and the water, fat, protein, and carbohydrate contents of the adults after FTR treatments. Compared with that at constant temperature (20 ℃), the cold tolerance of the adults at 4 ℃ 22 h/20 ℃ 2 h and 4 ℃ 46 h/20 ℃ 2 h after 1 week enhanced significantly. The SCP and FP after FTR presented a downtrend, being the lowest (-26.38 ℃ and -25.51 ℃, respectively) for the female adults after 1 week of 4 ℃ 22 h/20 ℃ and the lowest (-26.82 ℃ and -26.38 ℃, respectively) for the male adults after 1 week of 4 ℃ 46 h/20 ℃ 2 h. After FTR, the carbohydrate and protein contents of the female and male adults increased while the fat and water contents were in adverse, with distinct changes after 1 week of 4 ℃ 22 h/20 ℃ 2 h and 4 ℃ 46 h/20 ℃ 2 h. The results indicated that FTR could enhance the cold tolerance of A. gifuensis adults, which was closely related to the variations of the biochemical substances in the adult body, and the treatments 4 ℃ 22 h/20 ℃ 2 h and 4 ℃ 46 h/20 ℃ 2 h for 1 week were most advantageous to the survival and practical application of A. gifuensis.