Abstract: As a kind of underwater unmanned combat platform, the extra-large unmanned underwater vehicle (XLUUV) can carry a large number of mission loads, and play an important role in the future underwater combat, which is attached great importance by various naval powers. This paper reviews the development situations and future trends of foreign XLUUVs, studies five types of foreign XLUUVs, such as ordinary type, submarine-like type, containable type and container type, analyzes the key technologies such as modularization, multi-domain communication, underwater detection, positioning and navigation, autonomous control and energy and power, and probes into its operational application in reconnaissance and surveillance, laying of lightning barrier, underwater attack and defense, and underwater delivery. It has certain reference significance for the development and application of XLUUV in China.