The invention relates to a permanently modified phosphogypsum composite thermal insulation template and a manufacturing method thereof. The composite thermal insulation formwork is prepared by coating the outside of the extruded board (1) with an interface agent (2), then coating the outside with a modified phosphogypsum slurry (4), and filling the middle of the modified phosphogypsum slurry with a reinforcing material (3). Modified phosphogypsum slurry is made by mixing calcined phosphogypsum powder, cement, fly ash, quicklime, slag micropowder, vitrified microspheres, latex powder, water reducer, retarder, etc. in a certain proportion and then mixed with water. The invention has the advantages of simple preparation process, fast forming, large output, time-saving, labor-saving and labor-saving, and most of the raw materials used are solid waste, which conforms to national policies, is energy-saving and environmentally friendly, and has remarkable economic benefits.