An analysis about the wavelength-division multiplexing isolation filter using concatenated long period chirped fiber grating by transmission matrix method is given. The key factors of design high performance of such type filter are proposed. The simulation result demonstrates that such type isolation filter have a very large band width, equal frequency spacing, high isolation, and with a neglect dispersion in the band pass, and the frequency spacing can be tuned by tuning the fiber length between the concatenated long period chirped fiber gratings.