The invention discloses a nanocomposite diatom ooze material and a construction method thereof. The material consists of a diatom ooze powder material and nano-titanium dioxide dispersion liquid, wherein the diatom ooze powder material consists of calcined diatomite, quartz sand, gray calcium powder, bentonite, wollastonite, seaweed gel, cellulose ether and negative ion powder. The construction method comprises the following steps of: mixing the diatom ooze powder material and water according to the weight ratio of 1:0.9 in the field; after stirring for 15 minutes by using an electric stirrer, performing batch-scraping coating texture modeling construction; uniformly spraying the nano-titanium dioxide dispersion liquid, namely photocatalyst solution to a construction surface by using a spraying gun after the surface is dried; and drying for 48 hours. By using the construction method, the problems that nano-titanium dioxide powder is difficult to disperse and easy to agglomerate, and has large additive amount, the production cost is high, and a nano-titanium dioxide material is wasted in the preparation process of the diatom ooze are solved, the functionality of the diatom ooze for purifying and decomposing harmful gases is improved, and the overall cost of the product is reduced.