With the rapid development of exploration in the ocean, identity authentication technologies have been applied in marine data transfer environments to address the challenges of security and privacy. However, sending data directly to the target server is often challenging during the process of offshore data transmission. Therefore, relay nodes are utilized to assist the data transmission. To guarantee data security in this situation, a multilevel data transmission identity authentication protocol (AIAS-oceanMT) is introduced in this paper, which is tailored for the complex network conditions in the marine environment. Based on elliptical curve and digital signature technologies, two stages of authentication as identity authentication and data authentication are offered. During data processing, only XOR operations, hash computations, and Elliptic Curve Cryptography (ECC) operations are used, also, efficiency and security are effectively balanced. The security of our protocol is supported by a Real-or-Random (ROR) Model. Furthermore, lower communication and computational overheads is demonstrated from our protocol in comparative analyses on security feature with other protocols, which is confirmed by the simulate experiment.