ln the infrared communication characteristic experiments, the optical constants of materials can beobtained by measuring the relleetivity and transmissivity. However, the existing approximate solution methodshave errors ,and therefore the experiment can only measure materials with small or large attenuation.To solvethis problem ,the analytical solution is obtained by solving the equations,The extinction coeficient , attenuationcoelicient and relractive index of the material can be direelly ealculated from the analytieal solution. Theimproved calculation method has greater universality.