出处：按学科分类—语言、文字 中国对外翻译出版公司《汉英成语词典》第238页（227字）
包围敌占城市以引诱敌人来援，然后以主力歼灭敌人的援兵，例这一仗必须采取围城打援的战略才能取胜。
In order to win this battle，we have to annihilate the enemy's reinforcements who are on their way to relieve their besieged town．