The design method of long-wave athermal lens is discussed. The new chalcogenide glass material is adopted in the design of optical system. The characteristics and applications of the chalcogenide glass are introduced. The design method of athermal optical lens is analyzed. And the long-wave infrared athermal lens with chalcogenide glass is designed on the basis of technical requirements. By matching the chalcogenide glass with other infrared materials reasonably, through system optimized design, a better imaging effect is obtained in a wide temperature range.