A preparation method for warm-keeping mortar is disclosed. The mortar is characterized by comprising, in parts by weight, 500-1000 parts of cement, 0-200 parts of mineral powder, 0-150 parts of fly ash, 0-100 parts of talcum powder, 0-100 parts of heavy calcium powder, 0-50 parts of silica fume, 0-100 parts of an expanding agent, 0-1 part of an early strength agent, 0-2 parts of PP fiber, 0-2 parts of wood fiber, 0-30 parts of latex powder, 0.5-8 parts of cellulose ether, 0-3 parts of a water repellent, 0.001-0.2 part of an air entraining agent, 1-4 parts of a water reducer, 0-2 parts of starch ether, 0-2 parts of a retarder, 2-500 parts of a lightweight particle, and 400-1000 parts of water. The warm-keeping mortar possesses good fluidity and fluidity maintenance property, good wrapping property, good durability and high strength. The product can be produced as dry-mixed mortar, also can be produced as wet-mixed mortar in a wet-mixed mortar production line or a concrete stirring station, is used by being transported to a building site by utilizing a tank car, and accords with the current-stage environment protection requirements of saving energy and reducing emission and preventing dust. The mortar is good in plasticity, is applicable to exterior-wall warm insulation, indoor baffle walls, roofs and the like, and is wide in application scope and low in cost.