Defensiveness is a pivotal characteristic of traditional military settlements in ancient China, influenced by various factors linked to settlement construction and the occurrence of battles. Previous studies have typically focused on specific periods or moments, overlooking the dynamic interrelationships that evolve over time. The study proposes the concept of ‘defensive efficiency’ as a specific indicator for measuring the level of military defense system construction. Meanwhile, the analytic hierarchy process (AHP) was introduced to decompose the complex defense efficiency indicators into a quantitative system consisting of four levels of evaluation factors, analyse and statistically analyse the individual evaluation factors, and finally integrate and visualise the comparison of the data over multiple periods of time with the help of a geographic information system (GIS). The results of the study show that the changes in defensive efficiency in the four periods reflected the four stages of coastal defense construction in Ningbo during the Ming Dynasty: the preliminary construction period, the full construction period after repeated Wokou infestations, the basic completion period, and the period when Wokou encroachments were reduced and the point of attack was relocated to the south. While the spatial distribution of battles drove the continuous construction and improvement of coastal defense settlements, the improvement of the coastal defense system had an obvious effect on resisting Wokou intrusion. The study enriches the understanding of the cultural significance of traditional Chinese military settlement systems, emphasises the importance of tailor-made strategies appropriate to different historical periods and regional contexts, and provides a basis for the sustainable conservation of extant remains.