A novel Underwater Acoustic Covert Communication Scheme based on sparse multiple access (SCMA) is proposed to solve the problems of high bit error rate (BER) and low spectrum utilization in traditional covert underwater acoustic communication. The scheme generates new SCMA codewords at the transmitter using Eisenstein integer and Logistic chaotic sequences, and then a codebook via a mapping matrix. At the receiving end, the original information is recovered by multi-user Detection Algorithm and decoding. Finally, the feasibility of the scheme is verified by experimental simulation, and the influence of different number of users on the performance of underwater acoustic communication is analyzed. At the same time, the sparse multiple access communication scheme is compared with the spread spectrum communication scheme, the simulation results show that the former has lower bit error rate and better performance.