Abstract: Slag has slow hydration rate and low activity at low temperature.To significantly improve the activity of slag at low temperature,the effect of physical flour grinding on the particle size of slag,compressive strength of slag slurry,and the effect of chemical activator on the compressive strength of the slag slurry were studied.After grinding,the specific surface area of the slag increased from 0.718 m2/cm3 to 2.181 m2/cm3,and the compressive strength increased from 0 to 6.6 MPa for cured slag at 10 ℃ for 24 h.The compressive strength of the slag slurry increased first then dropped as the amount of chemical activator JFJ-1 increased,and the optimal percentage of JFJ-1 is 4%.The compressive strength of the low density slag cement system of 1.30 kg/L reached 6.8 MPa with JFJ-1 cured at 10 ℃ for 24 hours,and the permeability of the cement was 0.014 5 mD.The compressive strength of the class G cement system with the density of 1.92 kg/L reached 1 MPa after cured at 10 ℃ for 24 hours,and the permeability of the cement was 0.044 2 mD.Both physical flour grinding and chemical activator can improve the activity of the slag at low temperature.