Abstract: In underwater acoustic communication, the traditional wideband Doppler estimation method is difficult to accurately track the time-varying Doppler factor, so the compensation performance of orthogonal frequency division multiplexing (OFDM) in the variable speed communication scene is poor. To solve this problem, a Doppler estimation and tracking algorithm based on null subcarriers is proposed in this paper. Firstly, the Doppler prior values are obtained by Chirp-Z transformation of the three-frequency signal, and then the estimated optimal carrier frequency offset (CFO) values are converted into broadband Doppler factors by using the null subcarriers combined with the CFO search compensation technology in OFDM notation. Then the acceleration of the current symbol is calculated and the speed of the next symbol is predicted. By updating the acceleration, the predicted value is corrected to realize the Doppler estimation of each OFDM symbol. Numerical simulation and lake test results show that the proposed algorithm can not only track Doppler changes effectively, but also has good compensation performance under constant and variable speed motions. Moreover, it has low requirements on frame structure design and is insensitive to prior errors, which is conducive to the engineering realization of underwater acoustic communication system.