This thesis emphasize on frequency synchronization for OFDM in very high mobility environment. The very high mobility environment for TAIWAN HIGH SPEED RAIL (300km/hr) leads to critical doppler effect, so the channel will cause fast fading and multipath interference (doubly selective channel).The mismatch between transmitter and receiver and doppler effect will bring about carrier frequency offset. In order to working OFDM technique in very high mobility environment, we propose multiple sections training symbol method、weighting method and prediction mode method to resist time-variant channel and then do carrier frequency offset estimation。After we finish carrier frequency offset estimation, we do frequency compensation to reach whole frequency synchronization.