In order to overcome the problems of transmission capacity and Doppler frequency shift in high-speed environments, a novel high-speed railway mobile communication two-layer link structure based on radio over fiber（RoF） and orthogonal time frequency space（OTFS） modulation technology is proposed. In the high-speed railway communication environment, wired part uses RoF technology as a solution for distributing high-frequency broadband wireless signals along the railway. The wireless part uses OTFS modulation to solve the problem of Doppler frequency shift （DFS） destroying the orthogonality between subcarriers of existing wideband orthogonal frequency division multiplexing（OFDM） signals by converting time-frequency domain signals into relatively stable time-delay Doppler domain signals. The simulation results show that under the same transmission conditions, when the bit error rate of OFDM modulation drops below 10-1, the bit error rate of OTFS modulation has dropped to the order of 10-4, and the transmission performance is better.