The reverse microemulsion method is a method for preparing silica sol by dissolving the silicon source in the oil phase, then adding a surfactant and an aqueous phase to form a reverse microemulsion, and then performing hydrolysis and polycondensation reactions. When preparing cationic silica sol, cations can be added to the reverse microemulsion to neutralize the negative charge inside the microemulsion droplets and on the surface of the silica sol particles to form a positively charged silica sol. The advantage of the reverse microemulsion method is that cationic silica sols with uniform particle size and good dispersibility can be prepared.