Abstract: Owing to its nonhomogeneity, anisotropy etc. geotextile / geomembrane composite,composed of PVC geomembrane and needlepunched geotextile, is a kind of engineering material with good thermal insulation, experiments are made on its thermal diffusivity.Simultaneously, combined with engineering examples, thermo-insulation of the geomembrane composite is computed and analyzed, and its results are verified.