The invention discloses a high-toughness cement-based composite wallboard with a photocatalytic function and a preparation method thereof. The high-toughness cement-based composite wallboard consistsof a photocatalytic coating layer and a high-toughness cement-based composite wallboard substrate, and the high-toughness cement-based composite wallboard substrate consists of the following raw materials in parts by weight: 90-130 parts of ordinary Portland cement, 90-130 parts of fly ash, 6-12 parts of sulphoaluminate cement, 10-18 parts of silica fume, 10-16 parts of micro beads, 4-6 parts of polymer fibers, 0-0.2 part of cellulose ether, 0.8-2 parts of an additive, 54-70 parts of water and 60-80 parts of superfine powder. Compared with the prior art, the composite wallboard has the advantages of excellent mechanical property and good durability, and the preparation method is simple and easy to operate. In addition, the prepared photocatalytic coating layer has excellent electronic transmission capacity, so that compared with other photocatalytic building materials, the high-toughness cement-based composite wallboard has a better photocatalytic degradation effect, and self-cleaningand high-efficiency removal of organic pollutants in the environment can be realized.