Commonly used infrared materials in the design of transmissive optical systems include ZnSe,BaF2 and LiF.In order to provide optical designers with accurate refractive index temperature coefficient parameters,a new method of relative measurement of the bias angle based on the auto collimation method is proposed,and a refractive index temperature coefficient measurement system based on infrared single point detection is constructed to analyze the accuracy advantage of the method.Experiments on ZnSe prisms are carried out by this system.And the experimental data are compared with the CHARMS system of NASA(National Aeronautics and Space Administration),and the relative error is within 1%.This system solves the practical problem of refractive index temperature coefficient measurement of infrared optical materials under wide spectral and temperature domain conditions,and further improves the measurement accuracy of infrared optical systems.