We investigate the problem of joint frequency offset and channel estimation for an 112Gbit/s QPSK CO-OFDM system. The paper presents a novel joint frequency offset and channel estimation method based on CP and training symbols. It is able to estimate the fractional part and integral part of frequency offset at the same time. Its estimation range is more than[-2,5 GHz,2.5 GHz] .Meanwhile, we present an efficient CD estimation and compensation method for CO-OFDM based on training symbol time-domain averaging (TSTA) and systematically investigate its robustness against transmission impairments such as the nonlinearity of MZ modulator, linewidth and frequency offset of laser. Simulation results indicate that even OSNR is very low, it estimates frequency offset and channel response very well.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.