The GNSS has been widely adopted in maritime ships, however, with the increasingly complex global situation, ports have assumed greater strategic importance during military exercises and other special periods, making them more susceptible to external interference. This can reduce the reliability of ships that rely solely on a single navigation system and may even result in GNSS receiver failure. Therefore, the problem of continuous localization and accurate target ranging for intelligent ships in ports under satellite-denied conditions has become a critical challenge restricting the development of autonomous navigation technologies. To address the practical requirements of intelligent ship navigation in port scenarios, this paper proposes an auxiliary localization approach based on prior port maps. On this basis, a target measurement algorithm is developed by constructing an adaptive ROI partitioning strategy for the shipborne LiDAR according to the ship′s navigation state. The proposed method enables rapid re-localization of intelligent ships and real-time, high-precision measurement of targets within navigable waters under satellite-denied conditions. Field experiments demonstrate that the proposed method achieves satisfactory performance in both auxiliary localization and ranging stability, with an APE of 0.058 m, STD of 0.044 m, and RMSE of 0.073 m. These results indicate a significant improvement in the robustness of intelligent ship localization in complex port environments.