The photonic crystal filters operating at three wavelengths of 850nm, 1330nm and 1550nm in optical communication are studied by using an optical transfer matrix method. How to let the filter operate at a given wavelength and has a extremely narrow band through the selection of the refractive index and width of each layer is also studied. Through calculation, the parameters of the photonic crystal filters operating at the above three wavelengths are obtained. The calculation results have shown that the centeral wavelength can move toward the long wavelength when the thickness of a defect mode is not changed. The extremely narrow band photonic crystal filters with a line width of 0,0001nm at the wavelengths of 850nm, 1330nm and 1550nm can be fabricated when the proper parameters are selected.