This study is aimed to solve the problems of weak mechanical properties and low degree of slag reaction when weak single alkali-activated slag cementitious material (AASM), and to alleviate the operational hazards of AASM. Therefore, a combined activator of Na2SiO3/Na2CO3 was used to investigate its influence on the setting time, compressive strength, hydration products and autogenous shrinkage of AASM. Moreover, the environmental benefit of AASM was assessed. The experimental results show that the retarding effect is significant and the compressive strength is reduced with the increase of Na2CO3 alkali dosage, whereas the reduction rate of compressive strength is slightly decreased as the hydration time increased. More types of hydration products are produced by adding Na2CO3. The amount of C-(A)-S-H increased first follow by a decrease with the increase of Na2CO3 alkali dosage, thus explaining the changes in the autogenous shrinkage. Furthermore, based on the CO2 emission index, the combined Na2SiO3/Na2CO3 activated slag is produced in a cleaner manner with greater environmental benefit, compare to the Na2SiO3 activated slag.