Based on photonic crystal oneway waveguide, one threeport system and two kinds of fourport systems were designed. According to coupled mode theory in time, it was confirmed that the channel drop filters on the basis of oneway waveguide have more simple structure than that with only general dielectric photonic crytal waveguides in order to achieve 100% channel drop efficiency, which is benefit to the solution to the fabrication difficulty of the devices. The simulation results calculated by the finite element method shows that the channel drop efficiencies are all over 90%, which does agree well with the theoretical analysis.