The invention belongs to the technical field of titanium dioxide performance detection, and particularly relates to a method for detecting the cleanliness of titanium dioxide in a water-based coating.The method comprises the steps of: a, uniformly dispersing cellulose, an assistant and water, and adjusting a pH value to 8.5-9.5 to obtain cellulose pulp; b, adding titanium dioxide into the cellulose pulp, and uniformly dispersing the mixture to obtain a water-based paint color paste; c, coating the water-based paint color paste on card paper by using an automatic coating instrument to preparea sample plate, and drying the sample plate; d, and observing a number of coarse particles on the sample plate under a D65 standard light source, calculating a proportion of the coarse particles in unit area, and comparing the sample plate with a standard sample to determine whether the product is qualified or not. The detection method provided by the invention can characterize the cleanliness oftitanium dioxide in a coating system more visually and objectively, and provides an important detection method for the market.