A new configuration of four-port channel drop filter in two dimensional photonic crystals (2D PCs) is presented. In this structure, three micro-cavities are used. Two micro-cavities are used to realize wavelength-selective reflection feedback. The other is used for resonant tunneling-based channel drop filter. Using coupled mode theory (CMT), the conditions to achieve 100% drop efficiency are derived. The simulation results by using the two dimensional FDTD method show a good agreement with the CMT results, and show that this configuration is feasible.