The invention discloses a nano titanium dioxide (TiO2)/montmorillonite composite photocatalysis water treatment material and a preparation method thereof. The material consists of the following raw materials by weight percent: 40 to 98 percent of nano TiO2 and 2 to 60 percent of montmorillonite, wherein the nano TiO2 is loaded on the montmorillonite. The preparation method comprises the following steps of measuring the nano TiO2 and the montmorillonite, uniformly mixing the nano TiO2 and the montmorillonite, and placing the mixture into absolute ethyl alcohol to obtain pulp; dispersing the pulp through ultrasonic, then placing the pulp into a ball milling machine to be mechanically ball milled to obtain a mixture; completely drying the mixture at a constant temperature; carrying out the heat treatment again on the mixture, then cooling the mixture to the room temperature, and taking out the mixture to be uniformly ground to obtain the water treatment material. The nano TiO2 is fixedly loaded on the natural mineral montmorillonite through a simple and environment-friendly solid phase dispersion method, so that the composite material has the characteristics of easy dispersion and convenience in recycling when the composite material is used in a liquid phase, the photocatalysis degrading capacity of the composite material in the range between the ultraviolet and the visible light can be improved, and the original characteristic of the montmorillonite for purifying the water also can be realized.