Through laboratory test under cyclic freezing and thawing, the sandstone of Kizil grottoes was reinforced by potassium silicate solution of different mass percentages and concentrations. The volume, mass, wave velocity and compressive strength of reinforced sandstone samples after freezing and thawing were measured, and the optimal concentration and mass percentage of potassium silicate solution were obtained. Results showed that potassium silicate solution of 25% mass percentage has the best strengthening effect because low mass percentage would result in inadequate cohesion whereas high mass percentage would lead to low friction and cohesion with no direct contact between particles. Higher concentration of potassium silicate solution leads to better strengthening effect. The loss of volume, mass, wave velocity and compressive strength of sandstone reinforced by potassium silicate solution of 20% concentration is the smallest.