In this paper, we present a novel coupling method, direct coupling method, for double metal-cladding waveguide which is free from using the prism, grating or other coupling elements. The double metal-cladding waveguide used in our experiment is a metal-dielectric-metal three layer structure. Through ATR scanning technique, we demonstrate that light could be directly coupled into the waveguide successfully with this structure. The direct coupling method not only avoids the difficulty of grating fabrication process in grating coupling method, but also the coupling gap adjustment problem in prism coupling method. The application of this coupling method keeps advantages of the prism coupling technique in the optical parameters measurement for thin films. It also has some extra advantages. Since high order modes could be coupled into thick film waveguide while it is hard for prism coupling technique, the thickness of thick films (0. lmm—lmm) can be determined. Moreover, light can be coupled at any position on the surface of the waveguide, thus it can be used to detect almost the whole area of the film. Our experimental results agree well with the theoretical prediction.