The effect of dosage and modulus of water glass on the early hydration and setting performances of alkali-slag cement is very important. The variation of hydration heat and setting time and compressive strength of the alkali-slag cement with its modulus and alkali content are studied. It is found that with the increase of modulus, the hydration heat decreases and the setting time prolongs gradually, and the compressive strength increases first, then decreases. When the dosage of Na2O increases, the hydration heat increases. And the setting time increases slightly and the compressive strength shows the trend of increasing. The reasonable modulus of water glass Ms is about 1.0~2.0, and the dosage is about 3%~6% of the mass of slag.