Abstract: The influence of the rugate filter index profile function parameters, such as refractive index amplitude, film thickness and reference wavelength on the minus filter transmission spectrum, were investigated. The results show that the refractive index amplitude affected on the rejection bandwidth, the depth of cutting band was influenced by the film thickness, and the position of cut-off wavelength was determined by the reference wavelength. The method that the minus filters using the Rugate theory designed was presented in this paper. In addition, some minus filters were designed using the Rugate theory.