The invention discloses a nm titanium dioxide inorganic surface treating method. The inorganic surface treating is performed when the nm titanium dioxide is in good dispersed state and the inorganic surface treatment effect is increased using the said method. The invention solves the flocculation and dispersion problem of nm titanium dioxide using ultrasonic field, mechanical agitation and film separation and phase integrating. During the process of treating the inorganic surface, on the one hand the nm titanium dioxide dispersion liquid is always under the action of mechanical agitation and ultrasonic, on the other hand, the impurity ions are continuously removed using membrane separation device, so as to make sure the inorganic surface coating reaction under the full dispersed state of the nm titanium dioxide.