Abstract: The formation of the ruling policy of “defending against potential internal hazards while ignoring external threats”,the military and political strategy of “not being diligent and far sighted”,and the cultural trend of thought of “distinguishing between Huaxia and barbarians” in Northern Song Dynasty were closely related to the policy changes of the ruling class towards Yanyuns economic strategy.In the process of dealing with the surrounding ethnic relations and reshaping the order of China during the early Song Dynasty,the changes in the strategy of the Song Taizong Dynasty to the sixteen prefectures of Yanyun were the most prominent,from the expedience of making peace with the Liao to the strategic progress of “fighting”,from the northern expedition aimed at Youji to the political vision of “retaking at different times”;after the failure of the second northern expedition,the strategic retreat of “agreeing on the territory of Huarong and permanently stopping the war” replaced the previous active advancement of “directly targeting the enemys territory or military objectives,and completely destroying enemys camps or important military facilities”.Under the political explanation of “good soldiers,ominous weapons,and the sage had no choice but to use them”,the internal defense route of “defending against potential internal hazards while ignoring external threats” and “not being diligent and far sighted” was thus established.Emperor Zhenzong of Song Dynasty inherited this political line and frontier defense strategy,and eventually signed the Chanyuan Treaty with Liao Dynasty,and realized the idea of “negotiating the border of Huarong” with Liao Dynasty in the practical field.

Key words: Song Taizong, sixteen prefectures of Yanyun, Yongxis northern expedition, defending against potential internal hazards while ignoring external threats