Abstract: The slow-freeze-thaw cycle test was carried out on 72 nano carbon fiber/concrete specimens with 6 different nano-carbon fiber contents, the effects of nano-carbon fiber content on the anti-freezing performance of nano carbon fiber/concrete were studied by measuring the anti-flaking ability, mass loss rate, relative dynamic elastic modulus and compressive strength loss rate of nano carbon fiber/concrete after different freeze-thaw cycles. In addition, with the help of FE-SEM electron microscopy and mercury intrusion test, the improvement mechanism of nano-carbon fiber on the anti-freezing performance of concrete were analyzed from the microscopic level. The results show that nano carbon fiber can improve the frost resistance of concrete by improving the micro-morphology of concrete, refining its pore structure, improving its integrity and compactness, and improving the frost resistance of concrete. When the content of nano carbon fiber is 3vol%, the anti-freezing performance of concrete is optimized. Compared with ordinary concrete, after 300 freeze-thaw cycles, the relative dynamic elastic modulus of nano carbon fiber/concrete increases by 33.2%, and the anti-flaking ability is significantly enhanced. Under the same number of freeze-thaw cycles, with the increase of nano carbon fiber content, the relative dynamic modulus and compressive strength loss rate of nano carbon fiber/concrete shows a trend of increasing first and then decreasing, and the mass loss rate shows a trend of decreasing first and then increasing. However, when the nano carbon fiber content is up to 5vol%, the frost resistance of nano carbon fiber/concrete is still better than that of ordinary concrete, and the more the number of freeze-thaw cycles, the more significant the effect of nano carbon fiber on the antifreeze performance of concrete.