In order to cope with the demand for positioning， navigation and timing (PNT) in the future complex battlefield environment and to build a more reliable PNT capability， China is vigorously promoting the construction of a national comprehensive PNT system with the third generation BeiDou Navigation Satellite System as the core， of which the underwater PNT system is an important part. The underwater PNT system is an important component. Since satellite signals cannot be received underwater， it is required to use inertial navigation system (INS) with higher accuracy as much as possible， and the atomic gyro has very high theoretical accuracy， which provides the possibility to build INS with high accuracy. Therefore， the structure and basic principle of atomic gyro technology from the perspective of underwater PNT system construction requirements are reviewed in this paper.Its development history， research status， problems and application degree at home and abroad are introduced， and the important role and application prospect of atomic gyro in the construction of underwater PNT system are analyzed.