Abstract: All levels of the Song Dynasty military generals, military theorists based on a large number of military struggle practice, summed up a lot of defense thoughts, especially the thoughts of active defense. There was specific performance in four aspects: the first policy is to resist the enemy’s thought; the second is to defend the attack, and have the thought of the combination of attack and defense; the third is to rely on the people, and arouse the people to action; the fourth is to change when the enemy changed, and change in advance of the enemy’s change. Under the guidance of these thoughts, the Song Dynasty achieved many victories in the battle of the city. However, due to the corruption of the military government in the Song Dynasty and the long-term passive defense strategy, these excellent operational ideas have not fully played their due role.

Key words: Song Dynasty, city, active defense