The non-ideal frequency response and power fading phenomenon caused by optic-electric device in the transmission link of a direct-detection optical orthogonal frequency-division multiplexing (DDO-OFDM ) system are theoretically analyzed.In order to reduce the influence of the non-ideal frequency response and power fading phenomenon, a digital pre-distortion technique for power fading of OFDM signal subcarriers is proposed. We compare regular OFDM signal with the pre-distorted OFDM signal in a DDO-OF DM system.The experimental results show that the power of high freque ncy subcarriers of the regular OFDM signal is attenuated severely after 200km standard single-mode fiber (SMF) transmission ,but the spectrum is relatively flat by pre-distorting the power of the OFDM s ubcarriers at the high frequency.In addition,the received sensitivity of the pre -distorted OFDM signal is significantly improved by about 3dB at a bit error rate of 1×10－4 co mpared with the regular one without this technique.It is demonstrated that this pre-distortion technique can improve the system′s performance effect ively.