Based on the resonant coupling principle between the defect mode of micro-cavity and the waveguide mode, a new multi-channel drop filter is designed using the two-dimensional square lattice photonic crystal. The filter is composed of the bus waveguide, the 90° bend waveguide and the resonant micro-cavitiy. Every channel drop efficiency of the filter is enhanced greatly due to the perfect combination. The transmission characteristic of the filter is simulated with two-dimensional finite difference time domain method and theoretical analysis is performed in order to understand the important factors affecting the drop efficiency. The optimized device enhances the drop efficiency of every channel drop waveguide to over 91%. The simulation results show that the filter has the ability to download the light wave efficiently. The device has a good wavelength selection performance with the channel spacing of 20 nm, the center accordance less than ±2 nm and the maximal spectral half-width of 3.2 nm. It is demonstrated that the drop efficiency of the filter is improved greatly by increasing the coupling region between the download waveguide and the resonant micro-cavity.