When designing a cut-off interference filter, extra layers are needed to add on each side of periodicsymmetrical multilayer to match the incident medium and the substrate. In this paper, we use sol-gel film withadjustable refractive index as the match layer. The influence of the refractive index and thickness of the matchlayer on the film system is discussed in detail. As an example, a special filter which is transparent (>80%) at thewavelength 3-5μm and high reflective (>90%) at the wavelength 1.3μm is designed. Finally a series of optimizedfilm parameters are presented. The whole design process is a good reference to the other multilayer special filtermade by sol-gel process.