The timing synchronization methods for dc-biased optical OFDM system are different from wireless OFDM system because dc-biased optical OFDM system use intensity modulation/direct detection. Existing synchronization methods cant be used directly in dc-biased optical OFDM system. Therefore, the new timing synchronization method for dc-biased optical OFDM system is presented. The simulation results show that this timing synchronization method increasingly improves the estimated accuracy of dc-biased optical OFDM system.