In this study, multiple techniques including calorimetry, thermogravimetric analysis, XRD, mercury intrusion porosimeter (MIP), ICP-OES and SEM were employed to establish quantitative relationships between hydration products and mechanical properties of cement mortars, which provides further insights into the mechanisms of aluminum sulfate (AS) and sodium aluminate (NA) influencing the strength development of cement mortars. Results indicates that, at the same dosage, AS and NA perform different mechanisms in affecting the early strength growth of cement mortars. AS does not significantly affect the sulfate equilibrium of the cement paste, whereas NA turns the cement paste into an under-sulfated system. NA significantly alters the dissolution-precipitation equilibrium of the cement paste. It is found that the compressive strength of cement mortars is affected by the hydration degree of silicate phase and the process of structure build-up. The early-age strength of mortar is not only derived from the amorphous hydration products, but also from the crystalline products such as AFt and AFm. Moreover, the formation of ettringite in early stage other than AFm is more conducive to the establishment of a good early-stage solid network structure of cement paste, thus promoting the development of its later strength.