The influence of ultrafine fly ash on sulfate attack resistance of cement concrete was studied, aiming to solve the problem of sulfate attack of buildings at low temperature in Xinjiang. The mass loss rate and compressive strength performance of different cement concrete specimens were tested under the conditions of 30%, 45% and 60% ultrafine fly ash in the temperature of 5℃ and the sulfate erosion solution of 5%. The experimental results showed that the mass and compressive strength loss of the blank specimens without fly ash were relatively very large under sulfate erosion, indicating that the sulfate attack resistance of the specimens without the addition of ultrafine fly ash was poor. There was no mass loss of cement mortar specimens mixed with ultrafine fly ash, and there was the positive correlation between compressive strength and erosion age. The addition of ultrafine fly ash could effectively improve the sulfate resistance of cement mortar, and with the increase of the content of ultrafine fly ash, the growth rate of compressive strength of cement mortar in sulfate attack solution also increased.