宋對遼之戰略，在雍熙北伐失敗後，逐漸轉向防禦之戰略。而鎮定高陽關三路行營即是宋真宗時期對遼防禦戰略之落實。北宋三路行營是因應當時局勢而建立，本文試由宋遼邊境的地理形勢，遼南侵之目的與戰略，鎮州、定州、高陽關三大戰區的形成與宋代陣法之實踐等層面，討論三路行營建置之背景與過程。

After the failure of Yon-si's Northern Expedition to the Liao Dynasty, the strategy of the Song Dynasty toward the Liao gradually became a defensive one. The three military installations: Jen、Ding and Gau-Yang Guan were all the implementations of the defense strategy of Emperor Zhenzong. The three installations were instituted for dealing with situations of that time. This article will discuss the background and processes of the installation of the three installations from four perspectives: the geographical situations at the border between the Song Dynasty and the Liao, the purpose and strategy of Liao's southbound invasion, the formation of three major war zones-Jen、Ding and Gau-Yang Guan, and the Song Dynasty practice of tactical formation.