Abstract: With the increased demand for underwater acoustic communication rate and the increase of users, high-speed underwater acoustic communication and effective share of spectrum resources become a hot topic in underwater acoustic communication research. Cognitive underwater communication is a new way to solve the spectrum resources sharing, and OFDM has advantages including high efficiency in spectrum utilization, faster communication speed and flexibility in choosing frequencies. After introducing respective advantages of the two techniques, the feasibility of adopting OFDM technology to cognitive underwater communication is proved. A design scheme of cognitive underwater communication based on OFDM, the block diagram and the simulation results are given. The results prove the feasibility and effectiveness of the OFDM based cognitive underwater communication.