The infrared gradient refractive index material has a large refractive index and a large refractive index variation, resulting in a high density and density variation of interference fringes. In order to accurately measure the infrared gradient refractive index material, a λ=10.6 μm infrared Mach Zehnder interferometer was studied, and a zoom and fixed focus synchronous imaging scheme was designed to solve the difficult measurement problem caused by dense stripes in the case of large gradient distribution of materials. The refractive index distribution of infrared gradient refractive index materials was obtained by measuring the transmitted wavefront. Using this interferometer, the axial gradient refractive index sample with a thickness of 2mm and the radial gradient refractive index sample with a thickness of 9mm were measured, and the refractive index changes of the two samples were obtained to be 0.305 and 0.053, respectively. Using this interferometer to measure the infrared gradient refractive index sample, the maximum steepness of the sample's refractive index change is 0.035. To verify the measurement accuracy of the interferometer, the transmitted wavefront of a 10mm thick silicon wafer was measured, and the results showed that the refractive index measurement error was in the range of 10^-5.