Based on defect mode theory and slow light effects, a new scheme of encoder/decoder in 2D-opticalcode division multiple acess (2D-OCDMA) which uses multi-channel photonic crystal (PC) filter is proposed. According to couple-mode theory, user signals were cut into several pulses in accordance with the address code sequence due to the defect resonator. Then, the frequency encoded of user signal in 2D-OCDMA can be performed. Because of the slow light effects of PC waveguide，the time delay of the structure in micron magnitude is up to nanometer magnitude, which comes up to the standard of correct encoding and decoding. The centre wavelength of the three-channel encoder of 2D-OCDMA are 1545.00, 1555.30 and 1570.60 nm respectively, and the time delay between dot defects is 0.4 ns. Without sidelobe in the transmission spectrum, there is no interference in decoding, which ensures the accuracy in the process of encoding and decoding.