The invention discloses a composite cement additive. The cement additive is prepared by mixing, by weight, 16-22 parts of calcium hydroxide, 10-16 parts of isopropanol, 8-12 parts of zinc chloride, 2-8 parts of 2-methyl-dodecane-5-one, 4-10 parts of dodecyl dimethyl betaine, 2-6 parts of lignosulfonate, 1-5 parts of alkyl succinimide, 6-10 parts of acetophenone, 2-8 parts of ammonium sulfate, 4-10 parts of tetrabutylammonium borohydride, 5-9 parts of palmitic acid and 6-12 parts of stigmastenol. The prepared cement additive can increase cement yield and enhance cement strength, has small influences on early-stage compressive strength of cement, can meet engineering requirements, can improve cement mechanical properties and a pore structure, improves anti-freezing and grinding assisting performance of the cement, reduces permeability of the cement, adjusts cement setting time, increases concrete compactness, and achieves the functions of energy conservation and environmental protection. Compared with additives sold in the market, the cement additive is remarkable in performance improvement and has wide market popularization prospects.