Abstract: In order to investigate the developing law of flexural strength of cement mortar under sulfate corrosion circumstances with low temperature, the sulfate corrosion tests were carried out under temperature of 20℃, 10℃ and 5℃, and the flexural strength of cement mortar under different ages was also tested. The results show that the flexural strength of mortar specimens increases rapidly first and then decreases, and it is obviously affected by the temperature. The lower the temperature is, the more serious the erosion is, which is mainly manifested by the decrease of the overall strength and the maximum value of the ascending segment decrease, and the beginning time of deterioration becomes earlier. Based on the Irassar model, a prediction model of flexural strength was proposed under sulfate corrosion circumstance at low temperature. The calculated value by the presented model is more consistent with the measured value than the existing model, and the maximum error is 9% and the average error is 2.3%. Therefore, it can be concluded that the proposed model can accurately predict the variation of the flexural strength for cement mortar under sulfate corrosion at a temperature range of 5-20℃.