A method for preparing a heat-insulating coating material specially used for environmentally friendly packages is disclosed. The coating material includes following main raw materials by weight: 25-35parts of waterborne silicone acrylic resin, 5-10 parts of polyphenylene particles, 6-12 parts of hollow glass microbeads, 10-18 parts of zirconia ceramic fibers, 6-10 parts of mica, 6-10 parts of SiO2 aerogel, 50-60 parts of ethanol, 2-3 parts of a dispersant, 1.5-2.5 parts of a coupling agent, 2-3 parts of a thickener, 1-2 parts of a defoamer and a [Ag<46>Au<24>(SC2H4Ph)<32>](BPh4)2 cluster. Themethod includes S1) pretreating the hollow glass microbeads, S2) pretreating the SiO2 aerogel; S3) preparing a powder material mixture; S4) preparing slurry; and S5) mixing the powder material with the slurry. Through synergistic effects of the raw materials, the prepared coating material has excellent flame retardance, excellent heat insulation performance and a high thermal insulation efficiency. The method is simple, the raw materials are easily available and environmentally friendly, and the preparation cost is low.