The invention belongs to the field of wall building construction inside and outside heat insulation, sound insulation and fireproof materials, and relates to inorganic mineral fiber spray rock mortar and a using method thereof. The inorganic mineral fiber spray rock mortar is prepared from, by weight, 60-65% of inorganic mineral fiber, 15-20% of fibrous sepiolite, 0.1-0.5% of hydroxypropyl methyl cellulose, 2% of redispersible latex powder, 0.5% of water repellent and 10-16% of Portland cement. The using method includes the steps that water is added into the inorganic mineral fiber spray rock mortar according to the weight ratio, the mixture is stirred into paste, and the paste is put into a sprayer for spraying; a wall is directly sprayed, inorganic mineral fiber spray rock mortar layers are formed at the two sides of the wall until the layers reach the design thickness; the surfaces of the inorganic mineral fiber spray rock mortar layers are decorated; compared with an existing inorganic mineral fiber spray heat insulation wall construction, A1-grade fire resistance is higher, sturdiness and weather fastness are better, and the defect that an existing inorganic mineral fiber spray heat insulation material has the single purpose of heat insulation in an outer curtain wall and a stone wall is solved.