The attenuated-total-reflections (ATR) of absorbing films contain much characteristic information about the films.Taking considerations of the prism coupling and film absorbing,the first-order perturbation theory is applied to deduce the simplified analytical expressions of the perturbed propagation constants.Based on the theory,a method is introduced for determining the complex dielectric coefficients and thicknesses by detecting and analyzing the attenuated-total-reflections of absorbing films.