Abstract: In order to study the fracture characteristics of cement mortar under the attack of sodium sulfate solution with different pH values,the material mechanics tests,the fracture tests of three-point bending notched beam and microscopic tests of cement mortar were conducted.Combined with the physical and mechanical properties,apparent morphology and microstructure characteristics of the eroded specimens,the evolution mechanism of fracture toughness of cement mortar under sulfate attack with different pH values was revealed.The results show that the evolution process of physical and mechanical properties,fracture properties and microstructure of the mortar specimens under sulfate attack with different pH values are different.When the pH values of the erosion solution are 7 and 3,the initial fracture toughness and fracture toughness of the specimens increase first and then decrease with the erosion time.After 180 days of erosion,the two fracture parameters reach their peak values,and after 270 days,they deteriorate by 58.4 % and 41.2 %,respectively.When the pH value of the solution is 1,the two fracture parameters of the specimens continue to deteriorate with the erosion time,and after 240 days,they deteriorate by 92.1% and 79.9%,respectively.As the pH value of the solution decreases,the mortar gradually changes from dissolution erosion and sulfate erosion to composite erosion dominated by acid erosion,and the erosion deterioration effect is enhanced.Under the same erosion solution,the fracture parameters of the specimens are linearly correlated with their tensile strength.The deterioration of the initial fracture toughness of the specimen is significantly greater than that of the unstable fracture toughness.