The invention discloses a nano-titanium dioxide/silicon dioxide aerogel modified polymer cement waterproof coating and a preparation method thereof. The coating is prepared from polyacrylate emulsion, sulphate aluminium cement, papermaking sludge ash, bamboo charcoal powder, sodium hexametaphosphate, 2,2,4-trimethyl-1,3-pentadiol monoisobutyrate, flatting agents, defoaming agents, wetting agents, butyl titanate, acetic acid, ethyl alcohol and nano SiO2 aerogel. The mechanical strength including bonding strength and tensile strength of the coating can be obviously improved; in nano TiO2 modified SiO2 aerogel, on one hand, the porous structure in the nano SiO2 aerogel has high adsorption to pollution gases in the air, nano TiO2 exerts a photocatalytic function and achieves an effect of trapping pollutants, and the photocatalytic efficiency is obviously improved; on the other hand, the hydrophobicity of the coating is improved, the wetting angle reaches 160 degrees or more, and the waterproof performance of the coating is greatly improved.