The pore size of cationic silica sol can be controlled by adjusting the reaction conditions and subsequent processing steps during the preparation process. For example, in the sol-gel method, the particle size and pore size of silica sol particles can be controlled by adjusting parameters such as the type and concentration of the solvent, the temperature and time of the hydrolysis and polycondensation reaction. In the reverse microemulsion method, the size and shape of the microemulsion droplets can be controlled by adjusting parameters such as the type and concentration of the surfactant, the ratio of the aqueous phase to the oil phase, and so on, thereby affecting the pore size of the silica sol.