In view of the phenomena that no Ca（OH）2 exsits in the hydration products of alkalislag cement and its carbonation is more serious, water glass was selected as the alkali activater, and XRD and SEM were adopted to study carbonation products and microstructure of alkalislag cement pastes, while the pore structure was researched by nitrogen adsorption. The results show that the carbonation takes place directly on the CSH gel and calcium carbonate, the carbonated product of alkalislag pastes exists mainly in the form of calcite. After carbonation, the Ca/Si of CSH gel decreases, while surface area of the pastes increases and the average pore diameter reduces. The change in cumulative volume of pores varies with modulus of water glass.