Abstract: To improve the reliability of mobile underwater acoustic (UWA) communication systems, a mobile underwater acoustic communication method based on orthogonal time frequency space (OTFS) modulation is proposed. Firstly, a low complexity cross domain Turbo iterative equalization algorithm is designed to deal with long delay spread of UWA channel, which performs minimum mean square error (MMSE) equalization on the received signal in the time domain, and transfers the external information to the delay Doppler domain for decode. Next, the decoded soft information of the delay Doppler domain is fed back to the time domain as a priori information for the next time domain equalization. From this, the iterative detection of equalization and decoding is implemented. In addition, in order to solve the problem of excessive complexity, a low complexity computation algorithm is adopted. The algorithm first uses diagonal elements of matrix to obtain initial estimation, then converts the matrix inversion problem into solving the error between the initial estimation and the accurate value, so that low complexity calculations can be achieved through iterative estimation of the error vector. The results of lake experiments show that the proposed method can achieve reliable performance at a maximum moving speed of 4 knots.