In order to make different frequency bands propagate along their own channels, three typical structures of channel drop filter (CDF) are designed in a 2-dimension dielectric rod square photonic crystal structure. Their performance characteristics are investigated by the finite-difference time-domain method， and transmission efficiency graphs of the their output ports are obtained. The maximal transmission power ratio of every channel is at a central frequency of pass-band, and the power ratios will decay swiftly when the frequency shifts towards higher or lower than the central one. These structures of CDF have the characteristics of excellent frequency selectivity, weak crosstalk among central frequencies of different bands, broad operating wavelength ranges, etc. They can be used to design micro devices such as narrow band-pass filter or band-stop filter. Therefore, the CDF has important application value in the design of optical path on a photonic crystal chip and wavelength division multiplexed optical communication systems, etc.