The invention relates to a geopolymer-based thermal insulation mortar with water resistance and fire resistance. The geopolymer-based thermal insulation mortar comprises, by weight, 96.2 to 112.1 parts of an aluminum silicon material, 28.4 to 33.1 parts of an alkali activator, 66.0 to 77.0 parts of a modified lightweight aggregate, 12.2 to 14.2 parts of a polymer emulsion, 0.2 to 0.4 part of a toughening component, 5.2 to 6.0 part of an additive, and 82.8 to 107.5 parts of water; and 0.28 to 0.42L of foam is added into each one kilogram of a mixture of the above raw materials. The geopolymer-based thermal insulation mortar possesses high consistence retention rate, low layering degree, low dry density, high strength, excellent water resistance, A grade fire resistance, excellent thermal insulation performance, and excellent cracking resistance; the service life of the geopolymer-based thermal insulation mortar is as long as that of buildings; and the geopolymer-based thermal insulation mortar is especially to be used for building exterior wall external thermal insulation.