Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier digital modulation technique. It's likely to be used in next generation high-speed railway communication system. When OFDM is used in the communication of high-speed railway user s, Doppler frequency shift will become an important technical barrier, because OFDM is sensitive to frequency offset. Especially in high-speed movement environment, Doppler frequency shift can destroy the orthogonal characteristic between subcarriers in OFDM system. In this paper, the authors analyze the performance of OFDM system in high-speed movement environment and propose a new Doppler spread estimation algorithm to improve the Bit Error Rate (BER) performance.