Abstract: This is an article in the field of ceramics andcomposites. C30 concrete was prepared with steel slag powder with different particle size as admixture, and the effect of steel slag powder particle size on the durability of concrete was studied. The test results show that the internal pores of concrete are mainly concentrated in 100~1000 nm, and the number of pores decreases with the refinement of steel slag powder, and the pores of about 10~100 nm increase with the refinement of steel slag. The addition of steel slag can improve the workability of concrete; With the continuous refinement of steel slag, the 7, 28 and 56 d compressive strength of concrete decreases first and then increases. The 56 d compressive strength decreases from 50.4 MPa to 37.8 MPa and continues to increase to 40.32, 42.84, 45.36 and 48.4 MPa. With the fineness of steel slag from 23.1 MPa decreases to 16.8、12.2、10.1、4.2 μm. The activity of m steel slag increased from 75% to 96%. After 100 freeze-thaw cycles, the mass loss of concrete without steel slag group is 7.6%. When 30% steel slag is added, the frost resistance of concrete decreases. With the change of steel slag fineness, the frost resistance of concrete increases continuously, when the fineness is 10.1、4.2 μm, the mass loss is reduced to 7.4% and 6.1%. The addition of steel slag can promote the solidification and storage capacity of concrete to CO₂ and enhance the pressure strength of concrete. The finer the steel slag is, the stronger the carbonization resistance of concrete is.