Abstract: Carbon fiber reinforced epoxy matrix composites are increasingly used in ultra-low temperature environments. However, due to the mismatch of the thermal expansion coefficient between the epoxy resin matrix and the carbon fiber, the carbon fiber composite material will produce significant temperature stress in the ultra-low temperature environment, which will affect its service performance. Mesoporous SiO₂ (M-SiO₂) with a particle size of 100 to 160 nm and an average pore size of 4.24 nm was successfully prepared by sol-gel method, and M-SiO₂/epoxy resin composites were prepared by adding them to epoxy resin by three-roller grinding method. The test results show that the addition of M-SiO₂ effectively reduces the thermal expansion coefficient of epoxy resin and improves its mechanical properties. Specifically, at room temperature and 90 K, the tensile strength of epoxy resin with 10wt% M-SiO₂ reached about 98.56 MPa and 160.97 MPa, respectively, which was 27.07% and 26.02% higher than that of pure epoxy resin, respectively. In addition, with the increase of M-SiO₂ content, the thermal expansion coefficient of epoxy resin decreases gradually, and when 20wt% M-SiO₂ is added, the thermal expansion coefficient of M-SiO₂/epoxy resin composites decreases by 26.31% compared with that of pure epoxy resin. The transverse fiber bundle tensile (TFBT) test results showed that the TFBT strength of epoxy resin with 5wt% M-SiO₂ content was increased by 41.07% compared with that of pure epoxy resin, indicating that M-SiO₂ could effectively improve the interfacial bonding properties of resin/carbon fiber.