Abstract: In order to provide guidance for optimizing the particle distribution of steel slag powder in steel slag cement，the particle size characteristics of the steel slag powder and the corresponding cementing performance of the steel slag cement under different grinding time are studied. Then，the gray relational analysis method is used to calculate the correlation of the slag powder with various size and the slag cement mortar strength. The results showed that: with the milling time prolongs，the specific surface area of slag is increased and its activity is enhanced，thus resulting that the slag cement mortar strength and the bending strength have been improved. Slag powder particles smaller than 20 μm，especially 10 ~ 20 μm grain size play a catalytic role in the strength of slag cement mortar. That greater than 20 μm play an inhibiting role in the strength of slag cement mortar. In order to make slag cement owning better gelling properties，how to improve the content of -20 μm particles，especially 10 ~ 20 μm grain，while reduce +20 μm grains should be considered.

Key words: Steel slag, Size distribution, Cementing performance of steel slag cement, Grey correlation analysis