Based on the direct-current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) combined with code division multiple access (CDMA), a DCO-MC-CDMA system is built. When the Gold code and m-sequence are selected as spread spectrum address codes in the proposed system, their cross-correlation is worse than that of orthogonal codes owing to the limitation of the system structure, leading to a greater multi-user interference (MUI). The maximum ratio combining, equal gain combining, and orthogonal recovery combining (ORC) are used to derive the signal-to-noise ratio expression under the influences of additive white Gaussian noise, MUI, and limiting noise. The simulation model of the Monte Carlo bit error rate (BER) in MATLAB is established. The research results show that with the increase of the number of users, the MUI makes the system BER performance worse. In contrast, the ORC eliminates the MUI induced by the difference between subchannel gains, and thus the BER performance is the best. The BER performance of the DCO-MC-CDMA system with the Gold code is better, because the cross-correlation of the Gold code is better than that of the m-sequence in