The invention discloses an additive of a soilless spraying covering material and a preparation method of the additive and belongs to the technical field of refuse landfill treatment. The additive is prepared from, by weight, 50-60 parts of phosphate tailings, 20-30 parts of humus and 20-30 parts of cement. The reverse flotation phosphate tailings are smashed into gravel with the diameter ranging from 5 cm to 20 cm, the gravel is put at the temperature of 900-1,000 DEG C and calcined for 1.5-2 h, the gravel is smashed into particles with the grain diameter ranging from 10 mesh to 20 mesh again, the particles are mixed with the humus and the cement in proportion, and the additive of the soilless spraying covering material can be obtained. According to the additive of the soilless spraying covering material, the reverse flotation phosphate tailings can be massively utilized, effective phosphorus is enriched through the humus and the cement, the alkalinity of the additive is reduced, and the use effect of the covering material is guaranteed.