The light emitting diode (LED) has limited dyna mic range,significant nonlinearity and clipping distortion in visible light communication orthogonal frequency division multiplexing (OFDM) system.By using the characteristics of light source which has many wicks,the bandwidth of OFDM is divided into several sub-bands.Data from each sub-band is used to generate a single signal by the inverse fast Fourier transform (IFFT) and the single signal is input into eac h LED wick.Then the optical superposition modulation OFDM (OSM-OFDM) signal is formed by the superposition of optical signals from all th e LED wicks.The modulation index of every single signal is low with the same DC bias in OSM-OFDM system.So it effectively avoids the n onlinearity and clipping distortion caused by LED.In particular,the system bit error rate (BER) performance d ecreases at least by an order of magnitud e with high input power.The optimal DC bias of OSM-OFDM system is achieved by the principle of maximum effective signal to noi se ratio (SNR).And the suitable number of LED wicks is chosen based on the equation of effective SNR when a real system is designed.E xperimental results show that the BER performance of OSM-OFDM system has improved an order of magnitude than the direct current o ptical orthogonal frequency division multiplexing (DCO-OFDM) system.