Abstract: In order clearly to learn the regularity that sensitivity to variations in the input angle of incidence i of a rhomb-type achromatic quarter-wave phase retarder vary with refractive index n,the total reflection phase transformation formula are used to deduce the transmissivity formula of sensitivity to variations in the input angle of incidence i of retarders and refractive index n and draw the theoretical curves.The result indicates that retarders are more sensitive to variations in the input angle of incidence i with refractive index increasing.So the higher refractive index material should be avoided in designing retarders.This application is advantageous in analyzing error in phase retardance measurement.