A real-time measuring method based on the ATR technique is proposed. The experimental setup consists of a laser diode as the optical source, a spatial filter as a beam expander, a CCD detector as a camera and a coupling prism, when a converged light beam which is transmitted through the spatial filter incidents upon the hypotenuse face of the prism, the reflected divergence spot imaged by the CCD camera will embody a black line in the case of the angular width of the light beam contains a coupling angle corresponding to guided wave resonance, several dark lines corresponding to the guided-wave modes are demonstrated on the computer screen. The dark lines move when some parameter of guide wave change, according to the shift of the dark lines, the refractive index and the film thickness of the polymer can be determined. This experimental setting can be used widely such as the wave-guide fabricating, detecting the poling process etc.