Channel estimation has a very importan t impact on the performance of the coherent o ptical orthogonal frequency division multiplexing (OFDM) system.The physical eff ects of optical channel,such as chromatic dispersion,polarization mode dispersio n,can be obtai ned through the channel estimation at the receiver by transmitting known data at the transmitter,The origi nal signal then can be restored through the equilibrium technology.This paper co nducts the mathematical analysis of the realization of channel estimation after presenting the coherent optical OFDM system,and applies minimum mean square erro r (MMSE) and improved MMSE algor ithms on our built coherent optical OFDM system simulation platform to study the performance of our channel estimation algorithm s.The results show that the MMSE and improved MMSE algorithms are able to enhanc e the performance of coherent optical OFDM transmission system,and have 2dB opt ical signal-to-noise ratio (OSNR) gain compared with l east square (LS) algorit hm at the bit error rate (BER) of 10－3.Th comple xity of the modified MMSE algorithm is two orders of mag nitude lower than that of MMSE algorithm.