Rapid freezing thawing tests of concrete were conducted in laboratory after different carbonation times. The mechanical properties and microscopic pore characteristic parameters were investigated， and the concept of “pore sinuosity” of concrete was put forward. The test results indicate that carbonation contributes to enhance frost resistance of concrete， the 314 days carbonation can make dynamic elastic modulus of concrete reduce at least 3%12% due to freezing thawing cycles. Carbonation increases pore sinuosity of concrete. Moreover， fly ash can also enlarge pore sinuosity of concrete， and erosion mediums seepage path becomes longer， thus the frost resistance of concrete is enhanced. The correlation between air entraining and pore sinuosity of concrete is loose， which shows that the mechanism of frost resistance affected by air entraining and mineral admixture for concrete is different.