A broadband band-stop filter based on a multiple side-coupled metal–dielectric–metal slots waveguide is analytically designed and numerically investigated. Beginning with a single-side-coupled slot, we use the dispersion equation and resonant condition to locate the stop band at the visible regime and achieve a narrow stop band filter. Then, we cascade several slots to enlarge the stop band to 2.5 times wider than the single-slot condition. Next, if the height of the slots is gradiently distributed, multiple stop bands will exist. Finally, as a refractive index sensor, the figure of merit of this structure as a sensor reaches . This optimization design process significantly paves the way for high efficient filter or sensor production and fabrication in the visible range in practical scientific or engineering works.