Reflection filters have important application in optical communication, optical imaging, and hyperspectral remote sensing. This paper intendes to design a reflection multichannel filter consisting of metal and dielectric films on the basis of the unique characteristics of one-dimensional photonic crystals with defects and the corresponding band gap theory. The working frequency range of the multichannel filters can be calculated by photonic band gap theory. The number of channels is determined by the number of periods of the “photonic crystal” defects. The channel positions can be established through the equivalent phase thickness method. Compared with the conventional design method of reflection filters which is mainly based on experiences, this design method based on the photonic band gap theory can find the design idea and theoretical interpretation of the multichannel reflection filter from the point of “photon”.