Abstract: According to the effects of low temperature exposure on the mechanical properties of carbon fiber/epoxy (CF/EP) composites, the tensile properties of TR50S/YPH-69 were selected after low temperature of 0℃, −20℃, −40℃, −60℃ for 100 h, 200 h, 300 h, 400 h and 500 h to investigate the effects of low temperature, then the damage mechanism of material was analyzed by SEM. Based on the test results, a prediction formula was proposed to predict the residual strength of CF/EP composites exposed at low temperature. The test results present that after experiencing long time cryopreservation, the tensile mechanical properties of CF/EP composites increase first and then decrease, with the increase of the low-temperature exposure time. When the exposure time at low temperature is less than 300 h, the tensile strength of CF/EP composites increases first and then decreases as the temperature decreases; after the exposure time exceeds 300 h, the tensile strength gradually decreases as the temperature decreases. And the tensile elastic modulus of CF/EP composites shows a gradual upward trend with the increase of low-temperature exposure time, the lower the temperature, the more obvious the upward trend. SEM analysis shows that after a short period of low temperature exposure, the fiber and epoxy resin bond stronger, which is conducive to load transfer and enhance the CF/EP composites’s tensile ability, the destruction morphology is represented by more resin wrapped on the fiber. After long-term exposure to low temperature, material may occur cracks due to different contraction coefficient. Under the applied load, the crack gets further spread, which is not conducive to the load transfer, and causes the tensile strength to decline. The failure morphology shows that the fibers agglomerate into bundles, and the fiber bundle spacing increases. Based on initial test, a formula of predicting the residual strength of CF/EP composites after low temperature exposure was proposed. The test results are in good agreement with the predicted results. The number of tests can be reduced, due to consider the equivalent effect of the same material under different low temperatures and exposure time.