The invention discloses a non-burning decorative glaze for building exterior walls, and a preparation method thereof. The glaze comprises ultrafine ordinary Portland cement, emery, nano-silica, redispersible latex powder, a superplasticizer FDN, calcined gypsum, alum powder, a natural mineral pigment, lithium carbonate, calcium lignosulphonate, a film forming aid, ethylene glycol, a defoamer and water. Compared with existing real stone paints and coatings, the non-burning decorative glaze for building exterior walls has the advantages of good fireproof property, good acid and alkali resistance, non-toxicity, tastelessness, high strength, high hardness, high tensile bonding strength, richness in color, strong adhesion ability, no sand drop, low construction environment requirements, fast solidification speed, long service life, no whitening or yellowing and no soft coating layer, can replace the novel building exterior wall non-burning decoration glazes of the existing real stone paints, and has great economic and social benefits.