The invention discloses a preparation and construction method of machine-sprayed phosphogypsum lightweight plastering mortar. The machine-sprayed phosphogypsum lightweight plastering mortar is prepared from the following components in parts by weight: 75-85 parts of phosphogypsum, 10-15 parts of fine aggregate, 1-6 parts of an inert admixture, 4-8 parts of lightweight aggregate, 0.1-0.2 part of aretarder, 0.1-0.25 part of a water-retaining agent, 0.05-0.1 part of an anti-sagging agent, 0.1-0.3 part of an enhancer, 0.2-0.8 part of a fiber and 0-2 parts of a brightener. According to the preparation and construction method, phosphorus building gypsum (mainly composed of calcium sulfate hemihydrate) modified from solid waste slag phosphogypsum generated when phosphorite is treated with sulfuric acid in the process of phosphoric acid production is used as the main raw materials to prepare the machine-sprayed plastering gypsum mortar, the raw material cost is lowered, the construction efficiency and the construction quality are improved, the purpose of turning waste into treasure is achieved, great economic and social benefits are achieved, and the machine-sprayed phosphogypsum lightweight plastering mortar has a broad application prospect in construction engineering.