In order to solve the problem of navigation support capability degradation in the absence of satellite navigation in ship formation, the method of multi-ship joint navigation was proposed. The multi-ship joint navigation system was established by taking the ship with inertial navigation system as the mother ship and the ship only equipped with platform compass as the sub-ship. The mother ship obtained relevant information of sub-ships through measurement and calculation, and sent it to the sub-ships, so as to improve the reliability and effectiveness of navigation information of sub-ships, and thus to ensure the accuracy and continuity of navigation information of the ship formation. The results show that the positioning error of a single ship has a significant decrease after adopting the joint navigation method, which provides a theoretical reference for ensuring the navigation of the ship formation.