A synthetic method of a monodisperse nanometer mesoporous silica/titanium dioxide composite sphere is provided. A mole ratio of ethanol, water, a template, an alkali and a silicon source which are raw materials is (0-11.0):115:(0.05-0.5):(0.03-8.0):1. The mass of a titanium source is 1-10% of the mass of a liquid mixture of the titanium source and the silicon source. The composite sphere is synthesized rapidly through the method. The method is simple in process and short in preparation time. The particle size of a product synthesized through the method is controllable in a range from 20 nm to 200 nm. The inside and the surface of the composite sphere can be functionalized, so that the composite sphere has high theoretical research and practical application value in the fields of adsorption separation, catalysis, environment protection, microreactors, synthesis of sensing and nanometer materials, and the like.