Fast setting of AAS (alkali activated slag) cement is the biggest obstacle for them to be used in practical engineering. The setting property and strength development of AAS cement were investigated with respect to the fineness of slag, main parameter of activator, the concentration of effective composition as well as the kind and incorporation of retarder. The mechanism of fast setting of AAS cement was analysed by means of hydration heat test, nonevaporable water measurement and mercury intrusion porosimetry. Based upon the test results, the technique of controlling the fast setting of AAS cement effectively is discussed.