The viscosity and setting time of Na and Na+K silicate solution with different Si/M ratios and alkaline activated slag pastes activated by silicate solution were studied respectively. Combined with Fourier tranform infrared spectroscopy(FTIR) spectroscopy of silicate solution, the degree of polymerization of silicate ion in solution was studied. The results show that the lower the Si/M ratio of the silicate solution, the smaller the degree of polymerization of the silicate. The incorporation of a certain amount of K_⁺ in the sodium water glass system can reduce the polymerization degree of silicic acid ion in the system and significantly reduce the viscosity of the solution and the slurry, so that the alkali activated slag pastes can obtain better work performance. At the same time, at the lower Si/M ratio (Si/M ≤ 1.5), the K_⁺ can also extend the initial setting time of the alkali activated slag.