Abstract: Dzong is a special type of traditional architecture in the Tibetan culture area. Its main characteristics are of both military defense and administrative management functions. From the perspective of military defense, the systematical defensive design of Tibetan Dzongs in terms of the site selection, functional layout, defense construction and traffic organization was analyzed, and the military defensive design characteristics were expounded from three aspects: the hierarchical spatial layout, vertical spatial structure and transportation system for peacetime and wartime. Furthermore, the specific role and effect of the military defensive design for Tibetan Dzongs in actual wars were illustrated by a case analysis on the military campaign of fighting against British Army invasion the Gyantse Dzong. Finally, the military defensive design concept of Tibetan Dzongs and its significance to heritage protection were summarized.