Sidewall spalling caused by freeze-thaw cycles is the initial stage and main form of Karez failure. In order to explore the engineering characteristics of high modulus potassium silicate (PS) reinforced sidewall, frost heave and strength tests of PS modified Karez loess after freeze-thaw cycles were carried out. The results show that PS can significantly increase the initial frost heaving water content, and greatly reduce the frost heaving amount of the soil samples, but the frost heaving amount does not decrease with the increase of PS content, mainly because the location of pore water changes with the increase of PS content. With the increase of PS content, the shear stress-strain curve transits from hardening to softening. At the same time, the curve before yield presents the transition characteristics of upward convex to approximate linear to downward convex, which indicates that the soil texture gradually changes from friction type to solidified type. With the increase of PS content, the peak strength of the samples increases significantly, among which the cohesion increases greatly, because the internal friction angle decreases with the increase of PS content. 3% PS content is feasible in restraining frost heave and strengthening sidewall for Karez. The research results have certain theoretical and practical significance for the reinforcement of Karez sidewall.