The invention relates to powdered putty for an exterior wall prepared from ultrafine steel slag micropowder, belonging to the technical field of solid waste comprehensive utilization and chemical building materials. Ultrafine steel slag micropowder is used as a main raw material, and a certain amount of cement, desulphurization gypsum, talc powder, emulsion powder and water-retaining agent are added to prepare the powdered putty for the exterior wall after sufficiently and uniformly mixing. The powdered putty for the exterior wall takes industrial solid waste as the raw material, the production cost of the putty for the exterior wall is greatly reduced; the putty is in a powdered state, so that the putty is convenient to transport; the powdered putty for the exterior wall has a simple production process and is convenient to construct; and the powdered putty for the exterior wall has the characteristics of strong bonding force, no cracking, water resistance, alkali resistance and the like.