By adopting heat-stew steel slag(HSSS) as a contrast, this research studied the gas quenching steel slag(GQSS) grindability using fractal theory and grinding power index. The results showed that the two kinds of steel slag had a good fractal characteristic, and the smaller fractal dimension was, the better grindability would be. Studied on the fractal dimension and grinding time of the two kinds of steel slag as well as their specific surface areas, a conclusion drawn that with the extending of grinding time, the fractal dimension of them would be continuously increased. However, within the same grinding time, GQSS not only have a relevant good distributed particle structural and a smaller fractal dimension, but also have a better linear relation between specific surface areas and fractal dimension. By determining the grinding power index, the correctness of using fractal theory to study GQSS can be proved. Meanwhile, the result also shows that GQSS has a better grindability.