Underwater acoustic communication has the characteristics of multipath effect and frequency selectively attenuation. Aiming at these characteristics, this paper proposes a Multi-Rate model based on channel feature based on OFDM (Orthogonal Frequency Division Multiplexing) technology. With the frequency selectivity of underwater acoustic channel and the link distance, the optimal carrier frequency can be derived. The pilot in OFDM symbol can be used to attain the SNR of each sub-carrier, and the

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... optimal modulation mechanism can be determined by the preset threshold. So we can get the maximal transmission rate under different link distances. This model addresses the problem of ISI (inter-symbol interference) caused by multipath in acoustic channel, and improves the throughput as well as transmission efficiency in underwater sensor networks. The simulation results show that under different link distances, the theoretical bandwidth can be obtained by the frequency selectivity of underwater acoustic channel, different sub-bands and modulation mechanisms can be obtained by channel estimation, and finally the maximal transmission rate can be acquired.