The invention discloses a nanometer self-cleaning out-wall latex paint and a preparing method thereof. The nanometer self-cleaning out-wall latex paint is prepared from, by weight, 140-180 parts of water, 10-30 parts of propylene glycol, 0.5-1.5 parts of wetting agent, 3-8 parts of dispersing agent, 1-3 parts of defoaming agent, 1-3 parts of preservative, 10-25 parts of film-coalescing aid, 10-50parts of nanometer titania, 180-240 parts of titanium dioxide, 80-150 parts of heavy coarse calcium carbonate, 40-60 parts of wollastonite powder, 40-60 parts of kaolin, 280-350 parts of pure acrylicemulsion, 80-120 parts of organosilicone modification acrylic emulsion, 2 parts of multifunctional auxiliaries, 2-4 parts of thickening agent and 1-2 parts of flattening agent. Compared with the priorart, the nanometer self-cleaning out-wall latex paint has the advantages of having excellent weather fastness, alkali resistance, and artificial weathering aging resistance, the problems that paint is poor in water resistance, prone to cracking, stripping, fines removal and color changing, and difficult to clean are solved, and the nanometer self-cleaning out-wall latex paint is suitable for being used in various occasions, and has high application and popularization value.