The invention discloses a vacuum low-temperature testing device and method for an infrared lens surface shape, and the device comprises an interferometer, a collimator, a vacuum tank, an infrared lensassembly, a test tool, an objective table, a light source platform, a sealing window, a small-aperture diaphragm, and a dial gauge. The collimator is fixedly connected with the vacuum tank, and the interior of the vacuum tank is provided with the objective table. The objective table is provided with the test tool, and the infrared lens assembly is fixedly connected to the test tool and is alignedwith the axis of the collimator. The collimator is aligned with the small-aperture diaphragm through the sealing window, and the interferometer and the dial gauge are respectively arranged at the other side of the small-aperture diaphragm, and the small-aperture diaphragm is fixedly connected with the light source platform. Through the cooperation of the interferometer, the collimator, the vacuumtank, the infrared lens assembly, the test tool, the objective table, the light source platform, the sealing window, the small-aperture diaphragm and the dial gauge, the device eliminates the impacton a testing result from the collimator, improves the testing precision of a deformation quantity of the infrared lens surface shape under the vacuum low-temperature condition, and irons out the defects of conventional testing equipment.