In the scenario of integrated terrestrial and space information networks, the integration of satellite communication with terrestrial 5G is an inevitable trend. For Orthogonal Frequency Division Multiplexing(OFDM), a key technology of the 5G air-interface protocol, how to efficiently serve the Low Earth Orbit(LEO) satellite communication systems with limited frequency band resources has become a hotspot. In view of the high dynamics of LEO satellites, system channel characteristics, service variability, and most Doppler frequency shifts, a dynamic resource allocation strategy for OFDM in LEO satellite communication is proposed. Firstly, based on the 3GPP standard and the maximization of spectral efficiency, the subcarrier spacing is selected, and the transmission performance of the channel is ensured by eliminating inferior sub-channels before subcarrier allocation, and the number of cycles during allocation is reduced by clustering in multiples; then, the subcarriers are greedily allocated according to user demand and channel characteristics; finally, the power allocated to a single user is applied according to the proportional water-filling principle. Simulation results show that the algorithm can effectively adapt to the LEO satellite scenario, reduce the complexity of the algorithm, and improve the system capacity while still ensuring the fairness of user demand and transmission rate.