The invention belongs to a construction mortar material, and particularly relates to desulfurization alpha semi-hydrated gypsum self-leveling mortar. The conventional cement-based self-leveling motor has the defects of low construction efficiency, low strength, massive cement consumption in mortar and disadvantage to energy conservation and environmental protection. The desulfurization alpha semi-hydrated gypsum self-leveling mortar is prepared by uniformly mixing and stirring the following materials in parts by weight: 40 to 60 parts of desulfurization alpha gypsum, 4 to 6 parts of cement, 20-30 parts of quartz sands of between 40 and 80 meshes, 20 to 30 parts of quartz sands of between 80 and 120 meshes, 0.06 to 0.10 part of retarder, 0.06 to 0.08 part of a water reducing agent, 0.08 to 0.10 part of a water-retaining agent, 0.05 to 0.08 part of a defoaming agent, 2 to 3 parts of re-dispersible gelatin powder, and 22 to 24 parts of water. The desulfurization alpha semi-hydrated gypsum self-leveling mortar has the advantages of high early-stage strength, strong adhesive force with a substrate, no radiation, low emission of CO2, high construction efficiency, and resource utilization of desulfurization gypsum.