The transmission properties of the one-dimensional photonic crystals with defects were studied using the eigen matrix method, and a new kind of tunable optical filter is proposed in this paper. When the one-dimensional photonic crystals (L1H1)m have defects such as LcH2(L2H2)n, there will be a narrow transmission band in the gap of the photonic crystals, meanwhile the other transmission peak will weaken and disappear with the increase of the periodic number of the cover layer. When the thickness of the couple layer changes, there will be two regions with high transmittivity besides the edges of the photonic crystals gap. The properties of the high transmission band depend on the photonic crystals and the cover layers. When the photonic crystals gap is narrowed, the two regions will come near, which results in a wide transmission region about 150 nm. A new kind of tunable optical filter thus can be fabricated based on this phenomenon by the surface micro-mechanical technology.