The T700/HT280 composites were subjected to vacuum thermal cycling (-140-180℃,10-3 Pa). The mass loss rate, dynamic mechanical properties and low-speed impact of composites were tested before and after vacuum thermal cycling respectively. The visual observation, ultrasonic C-scan and finite element (FE) analysis were used to analyze, characterize and simulate the low-speed impact damage. The results show that the mass loss rates of T700/HT280 composites and matrix resin are increased rapidly and then level off with the increase of the number of vacuum thermal cycles, which is due to the gassing effect. After the vacuum thermal cycle treatment, T700/HT280 composites show some degree of post-cure, thermal aging and partial interface debonding. The main damage mode at low impact energy is that the matrix resin is compressed. However, matrix cracking and delamination are deemed as the damage mode at high impact energy. The FE simulation results are consistent with the experimental results. As the impact energy increases, the absorption energy of the composites is increased. Under the condition of 30-40 J impact energy, the absorption energy can effectively characterize the environmental damage effects of vacuum thermal cycle on composites.