The disclosure provides a broadcast-type underwater navigation positioning system and method, wherein the system comprises a base station network consisting of a plurality of underwater base stations distributed on a seabed and a to-be-positioned user terminal located underwater, wherein the underwater base station comprises a bottom-mounted sonar and an mooring sonar, the bottom-mounted sonar and the mooring sonar are connected through a cable and are configured for ranging and communication through an underwater acoustic signal, the mooring sonar is integrated with an inertial measurement unit I, and the user terminal is provided with a passive sonar configured to unidirectionally receive an underwater acoustic signal sent by the mooring sonar for ranging and communication. The underwater navigation positioning system and method disclosed in the present invention can expand the service range of the base station, increase the capacity of the user terminal and improve the precision of regional sound velocity products.