Abstract: A dry granulation experiment was done by means of a rotary cup atomizer for blast furnace slag instead of the currently used water quenching process because it is unable to efficiently recover the waste heat energy inside the molten slag. The influences of cup atomizer rotating speed, its diameter and molten slag temperature on the mean slag granule diameter and granules' mass distribution were investigated. The results showed that the mean granule diameter decreases with increasing rotating speed which will lead the slag granules to be far from the cup so as to make their mass distribution more uniform. The rotating speed 1000 r/min is actually a criterion, i.e., the mean granule diameter decreases with increasing cup diameter if lower than it, while the diameter is almost unchanged if higher than it. And the molten slag temperature has no influence on mean granule diameter and mass distribution of granules.