The design of infrared phase-shifting Twyman-Green interferometer is described. An automatic phase-shifting infrared interferometer whose aperture is Φ30 mm is developed. The computer software is programmed to fit the wavefront and evaluate the imaging quality of infrared optical system. The calculation accuracy of software equals to the similar softwares in the world. Several kinds of application of infrared interferometer--the quality of infrared optical system,the roughness of ground glass and the flatness of compact disk are reseached. The result show, the optical quality of the interferometric system is better than λ/25, the extended accuracy is better than λ/130, and the precision is better than λ/200(λ=10.6 μm).