The invention discloses a gypsum-based foam material with thermal insulation and a preparation method thereof. The material comprises the following raw materials in parts by weight: 55-70 parts of desulfurized gypsum, 5-15 parts of cement, 30-45 parts of slag powder, 0.6-1.5 parts of a composite activator, 0.3-1.5 parts of a water reducer, 0.05-0.1 parts of a retarder, 0.1-0.3 parts of a PP fiber, 0.5-1 part of rubber powder, 0.002-0.03 parts of hydroxypropyl methyl cellulose, 0.8-1.5 parts of calcium stearate, 2-5.5 parts of a foaming agent, and 40-55 parts of water. The preparation method comprises the following steps: except the foaming agent and water, other components are mixed according to the weight ratio with stirring for 2-3 minutes; the components are poured into water which is prepared at 45-50 DEG C according to the weight ratio and the raw materials are stirred for 1-2 minutes; the foaming agent is poured into with rapid stirring for 15-30 seconds; the raw materials are instantly poured into die, wall, ground, floor and roofing, and after quietly waiting, the foam material is foamed and heightened. The gypsum-based foam material with thermal insulation has the advantages of fast prehardening, high efficiency, heat preservation, heat insulation, good water resistance, low density, and high strength. The foam material is good for utilization of solid and waste resources, and has the advantages of energy saving, environmental protection, usage of green resources, and wide prospects.