In coherent optical orthogonal frequency division multiplexing (OFDM) communicat ion system,when the transmission rate of a signal reaches 100Gbit/s or higher,the influence of the channel beco mes a major limiting factor affecting system performance.At this time,the system is very sensitive to channel factor s,which requires an effective method to accurately track channel changes.Through the channel estimation,the p hysical effects of optical fiber, such as chromaticity dispersion and nonlinearity,can be obtained at the receiver through the transmitted known data at the transmitter,and then through the equilibrium to restore the original signal.Th is paper first introduces the coherent optical OFDM system,then builds a coherent optical OFDM system simulation platfo rm.On this platform, a DFT based and improved algorithm is applised to the coherent optical OFDM syst em for channel estimation.The results show that this algorithm can improve the performance of coherent optical OFDM transmission system,and has 1dB optical signal-to-noise ratio (OSNR) gain compared with the DFT algorithm at th e bit error rate of 10－4,and has 3dB OSNR gain compared with algorithm.