Cross-domain communication between sea and air plays a vital role in cross-domain collaborative operations and the establishment of cross-domain heterogeneous marine unmanned systems. Based on the different deployment methods of cross-domain communication systems between sea and air, this work introduces direct, relay, and conversion cross-domain communication technologies. The characteristics and limitations of various cross-domain communication technologies, both domestic and international, are summarized in terms of communication rate, communication distance, and deployment flexibility. Finally, the future research direction of this field is prospected.