A thermal insulation property measuring device, including a tank, a thermal insulator, a cuboidal frame, a support bracket, and a data collector. The tank includes an upper body, a first lower body, and a second lower body. The thermal insulator includes a first thermal insulation layer, a second thermal insulation layer, a first membrane, a second membrane, and a third membrane. The support bracket includes a trapezoidal support and a transition support. The tank is disposed on the support bracket. The support bracket is disposed in the cuboidal frame. The upper body, the first lower body, and the second lower body are spherical and communicate with each other. A filling tube, a pressure relief tube and a piezometer tube are disposed on the upper body. The first membrane is disposed on the tank. The first thermal insulation layer is coated on the first membrane.