漢代中央軍制常以南北軍制名之，然因史料寡少，自南宋以降存在二十餘說，但宋元間已形成主流觀點，並被近代學者當成定論。本文以為，諸說在學術史、軍制原理及漢初史事的檢視下皆難以成立，故考慮南北軍是禁衛卿校所領部隊以外的軍隊系統，並從漢初政局變化、社會背景、京城防衛兵力等方面探究其建置背景與軍隊性質等問題。概言之，高祖初定天下之際，猶有來自諸侯王國和匈奴的威脅，為兼顧京師安全並保有臨戰的機動性，或有若干精銳野戰部隊未解編，充任中央戰略預備軍。惠帝時期，備戰需求雖稍降，但都城防衛力量不足，故將高祖時期的臨時屯兵改編為南北軍，分屯於未央宮南北宮垣東段外圍。南北軍在組織和制度上雖尚未完全常備化，然這種由皇帝親貴或重臣以將相重銜督領屯兵、拱衛兩宮的作法，可說是昭宣以降中朝將軍領兵秉政之濫觴；而征伐軍職進入常備禁衛體系雖始於武帝新置諸校尉，然其源頭卻是漢初的南北軍。凡此或可視為漢初南北軍在兩漢禁衛體制發展脈絡中的制度史意義。

The imperial capital forces of the Han Dynasty (202 BC-9 AD) have often been called the Southern and Northern Armies (nanbeijun 南北軍). Due to the scarcity of historical sources, more than twenty competing interpretations have emerged since the Southern Song Dynasty (1127-1279). Among them, a dominant view, had already taken shape during the Song-Yuan period (12th – 13th centuries) and has since been regarded as orthodox by modern scholars. Yet these interpretations do not hold up well when examined according to their internal development, institutional principles of military system, and the history of the early Han Dynasty. Considering that the Southern and Northern Armies were separate from the troops led by the Imperial Guard system, the study explores the background of the institutional nature and the historical origin of the armies by taking into account changes in the political situation, social background, and the defense of the capital, etc.