蜀軍因為馬謖在街亭吃了大敗仗，軍力損失不少，諸葛亮只帶著五千名士兵，在西城搬運糧草。這時，突然聽到司馬懿帶領十五萬大軍過來，諸葛亮心想不妙，因為大將不在，士兵又有一半帶著糧草回去了，想一想之後，決定放手一搏。諸葛亮叫士兵把軍旗拿掉，四面城門全開，每扇門各派二十位士兵，扮成老百姓的模樣悠閒的打掃街道，其他人都不准隨便進出，更不可以大聲喧譁，否則一律斬首。接著，兩名書僮拿著琴跟著諸葛亮到城樓上，諸葛亮焚香後開始彈琴。當魏軍到達時，看到眼前的景象，沒人敢輕舉妄動，司馬懿到城門下觀望時，看到諸葛亮面帶笑容，專注的彈琴，城門口的老百姓也安靜的在掃地，完全感受不到快打仗的浮躁氣氛，琴聲也十分平靜祥和，司馬懿下令大軍立刻撤退，並對反對退兵的兒子說：「諸葛亮是一個做事謹慎小心的人，不會去冒這麼大的危險，一定是有伏兵，他才會如此悠閒的彈琴。」
三十六計之第三十二計：空城計
是一種大膽的心理戰術，當自己的實力相當弱的時候，故意表現出完全不設防的狀態，讓對方感到疑惑，以為是誘敵之計，反而不敢輕舉妄動。
The Shu army suffered a huge loss in the battle of Jie Ting where the general Ma Su lost the strategic city of Jie Ting and many soldiers. As a result, Jhu Ge Liang, the military advisor of Shu, only had five thousand soldiers left with him. While they were busy moving military supplies at 西城, news arrived that the enemy force of one hundred and fifty thousand troops, led by its general Sih Ma Yi, was heading towards them. Jhu Ge Liang thought this was bad news because his general Ma Su was not available and half of the soldiers had already gone back with the military supplies. In other words, they were extremely outnumbered by the enemy. However, after some contemplation, he decided to fight nevertheless.
Jhu Ge Liang ordered his soldiers to remove all the battle flags and had all four gates of the fort flung wide open. He then sent twenty soldiers to each gate disguised as civilians sweeping the grounds, acting nonchalantly. No one was allowed to leave the city nor talk in a loud voice. Anyone who acted against the orders would be executed on the spot. Then, he ascended the tower with two servants carrying his lute. After burning some incense, he started to play his lute.
When the Wei army arrived at the gate, the sight of a smiling Jhu Ge Liang playing his lute and the civilians quietly sweeping the grounds stunned them. No one dared to attack. It was all too quiet and peaceful. There was not the slightest anxiety of impending war. Seeing this, Sih Ma Yi ordered his troops to retreat immediately. He said to his son who was against the retreat, "Jhu Ge Liang is a thoughtful and resourceful man. He would not take such a huge risk. There must be an ambush waiting for us inside. This is why he played his lute with such ease and cool composure."
Strategy 32: The Empty Fort
This is a daring and highly risky strategy of psychological warfare. When your strength is relatively weak, drop all pretence of military preparation and act casually. The incongruity of the situation will confuse your enemy and make him believe that there is a trap waiting for him. This way, your enemy would be hesitant to advance.
