Achieving large system capacity is a challenge due to the narrow modulation bandwidth of the white light-emitting diode (LED) in visible light communication. The system capacity can be improved by the non-orthogonal multiple access (NOMA) technique which can reuse power. A NOMA-DCO-OFDM system which is a combination of NOMA technology and direct-current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) is proposed. Furthermore, a modeling method for VLC multipath channel is proposed based on the recursive method when a single LED is used. The signal to interference and noise ratio of users is derived when the clipping noise is considered. We also study the relationship among average sum rate of system, half power semi-angles of LED, field of views (FOV) of photoelectric detector and power distribution factor with methods of fractional order power allocation, gain ratio power allocation and static power allocation. The simulation results indicate that the average sum rate of system changes with the changing of half power semi-angles of LED, field of views (FOV) of photoelectric detector and power distribution factor, and the maximum average sum rate can be achieved when we optimize the half power semi-angles, FOV and power distribution factor.