The base-band bipolar optical code division multiple access (OCDMA) system is introduced, with transform of unipolar-bipolar and bipolar-unipolar, transmission of signal with bipolar codes is realized through unipolar medium. Gold sequence and m sequence in OCDMA system, and channel effect on the performance of OCDMA system are studied here. The simulation results demonstrate that Gold sequence and m sequence are adapted to bipolar OCDMA system according to the performance of the auto/cross-correlation, but Gold sequence in bipolar OCDMA system is better than m sequence. When the number of users is 20, the bit error rate (BER) is 10-9 for Gold sequence, and about 10-7 for m sequence. Channel model significantly influences the performance of the OCDMA system (～20 dB).