In this paper, the effects of cement content, water glass content and curing age on the impermeability performance of silty clay were discussed by indoor penetration test, scanning electron microscopy（SEM） and Xray diffraction（XRD） test on the typical silty clay in Nanchang. The results showed that the permeability coefficient of improved silty clay decreased at a rate of 3 orders of magnitude higher than that of 14~28 d at a curing age of 7~14 d. With the continuous increase of cement content, the permeability coefficient of improved silty clay decreased and the decline rate gradually decreased. The increase of water glass content can significantly reduce the permeability coefficient of improved silty clay. Cement-water glass can synergistically improve the impermeability of silty clay, and the optimal ratio of 24% cement + 6% water glass has an optimal dosage. Compared with the improved silty clay with single cement, the incorporation of water glass does not change the main phase composition of the hydration product, but promotes the hydration reaction, and increases the yield of hydration products such as C-S-H gel and C-A-S-H calcium vanadite, and greatly reduced the number of pores and fractures between soil particles.