Abstract: The military defense system along the Yangtze River in the Ming Dynasty,also known as “Jiangfang”,was the third largest national military defense system after border and coastal defense.Xindi is a product of the refined military space in Jiangfang,which evolved from the Xin Jiangkou Camp in the early Ming Dynasty with the expansion of its management scope.The selection of each Xindi location and starting and ending points follows certain military geographical principles.The barracks are generally set up in military fortresses or transportation hubs,and the upper and lower points of the Xindi are set up at natural boundaries or prefecture and county boundaries,making it convenient for the unified management of one barracks.The boundary between the Yangtze River and the coastal defense zone is precisely located at the tidal current limit of the Yangtze River Estuary.The management of important transportation hubs or military strongholds in Jiangfang adopts the method of crossing Xindi.For the social security issues on the river,the main method to deal with them is to increase the number of patrols in the areas where robbers are found in Shangjiang and Yingtian Prefecture.In Xiajiang,troops are stationed in areas where security issues are prominent or where merchants and civilians gather.The task of guarding against Japanese pirates is mainly the responsibility of the Chuanshan Camp and Sanjiang Camp.In short,both the site selection of the camp and the delineation of Xindi were based on the military situation at home and abroad in the early Ming Dynasty,the experience of the war that occurred on the Yangtze River,and the hydrological environment of the Yangtze River.Therefore,the defense effect was significant,ensuring the social security of the capital and the southeastern land of wealth.