Abstract: Pass-band filter based on a tunable cavity is designed in 2-dimentional square-lattice photonic crystal structure. Operational transmission bands of the waveguide and cavity system are adjusted by changing positions of tuning dielectric rods beside the 1×5 resonant cavity. The effects of input port coupling decay ratio and input port detuning factors on the filter are analyzed by using CMT(Coupled-Mode Theory). Wavelength transmission spectra of the filter are calculated with the help of FDTD (finite difference time domain) method. The results show that -3 dB band width Δλ of output 38 pass-bands ranges from 4.18 nm to 11.15 nm when the filter operates over 1320-1810 nm wavelength band. Pass-band peak wavelength tuning width of the proposed structure is 186.56 nm. The micro filter is suitable for optical telecommunication course Wavelength Division Demultiplexing(WDDM) system design and optical integration design etc.