The invention discloses a method for degrading methylene blue adsorbed in particles under solar illumination through titanium dioxide and belongs to the technical field of titania photocatalysis. The method is characterized by comprising the following steps that (1) a phosphoric acid solution is dropwise added into an aqueous solution containing citric acid and calcium hydroxide, hydroxyapatite is prepared, the hydroxyapatite is added into a solution containing the methylene blue, and a hydroxyapatite colloidal solution containing the methylene blue is prepared; (2) butyl titanate, nitric acid and polyethylene glycol are sequentially added into a mixed solution of ethyl alcohol and water, tartaric acid is added after water heating treatment, and a titanium dioxide solution is prepared; and (3) the titanium dioxide solution and hydroxyapatite colloidal solution containing the methylene blue are mixed and stirred, mixed particles are obtained through centrifugation and drying, and the methylene blue adsorbed in the particles can be degraded under solar illumination of 7-42 hours. According to the method, the process is simple, raw materials are low in cost, and industrial production is easily achieved. Degrading of the methylene blue can be achieved under solar illumination, and the degrading speed is high.