Athermalization is one of the important aspects of infrared optical system design. This article introduces the principle and method of athermalization design of infrared optical system using wavefront coding technology, analyzes the basic principles of wavefront coding, and gives the expression of modulation transfer function (MTF) of wavefront coding optical system. On this basis, the image quality of the three-plate long-wave infrared optical system at room temperature (+20 ℃), -40 ℃ and +60 ℃ is analyzed by using ZEMAX optical design software. The analysis results show that the imaging quality of the system is close to the diffraction limit at room temperature, but when the temperature changes between -40 ℃ and +60 ℃, the MTF value decreases rapidly and appears zero, indicating that the imaging quality of the system deteriorates sharply and no longer meets the requirements of use. The MTF value is no longer sensitive to temperature when the wavefront coding phase plate is added to the design of dethermal error, and a clearer target image can be obtained at different temperatures, indicating that the wavefront coding technology can realize the athermalization design of the infrared optical system.