The RF-pilot-assisted direct detection optical orthogonal frequency d ivision multiplexing (DDO-OFDM)system can effectively optimize the transmission performance by adjusting the carrier to signal power ratio (CSPR).It is regarded as one of the a lternatives for high speed and short distance local area network transmission.Based on the RF-pilot-assisted DDO-OFDM system archit ecture,a linear interpolation combined with time-domain average method is propo sed to estimate the channel response for non -pilot subcarriers according to the channel estimation results of pilot subcarriers.The channel estimation meth od can realize real-time tracking of the changes in the fiber channel and effectively suppress the noise influence by time domain averaging.In simulation,a 20Gbit/s RF-pilot-assisted OFDM signal is transmitted over 400km single mode fiber (SMF) with 13pilot subcarriers for channel estimation,and 4-quadrature amplitude modulation (QAM) is used for symbol mapping.The linear interpolation combined with time-do main average method is applied for the channel estimation of non-pilot sub carriers.There is almost no optical signal to noise ratio (OSNR) penalty after 400km SMF tr ansmission at bit error rate (BER) of 1×10－3 compared with back to back transmission results.We also conduct the proof-of-concept ex periment to verify the feasibility of the proposed method for the first time in RF-pilot-assisted DDO-OFDM syst em.