By adopting the quick freezing and thawing method and controling the air content of concrete in different amount of fly ash, the paper carried out 50 times of freeze-thaw cycle. The result shows that with the increase of air content of fly ash concrete , its frost resistance greatly increase and close to the frost-resistance of silicate cement concrete when air content is lower than 5%;when air content is from 5% to 15%，its frost-resistance is higher than that of silicate cement concrete.