Bao Xu was originally a bandit king on Kushu Mountain in Kouzhou. He had an ugly appearance, with a face shaped like the bottom of a wok, fierce bulging eyes and lips like a wolf's. He wielded a broad sword and excelled in martial arts. His only passion in life was to kill and plunder, thus earning him the nickname 'God of Death' (丧门神). He also had a thunderous voice which sent enemies trembling.
When the Liangshan heroes were attacking Lingzhou, Xuan Zan and Hao Si-wen were captured by Shan Ting-gui and Wei Ding-guo. They were escorted as prisoners back to Dongjing. Li Kui and Jiao Ting passed by Kushu Mountain and managed to persuade Bao Xu to join the Liangshan band. At that point, Hao Si-wen and Xuan Zan were being escorted past by the mountain. Bao Xu, Li Kui and Jiao Ting killed the guards and rescued the two heroes. Then, they went back to Liangshan together after Shan Ting-gui and Wei Ding-guo were subdued.
Bao Xu became one of the leaders of the Liangshan infantry and one of the 72 Earthly Fiends. After Song Jiang had obtained amnesty from the emperor, Bao Xu followed the heroes on their campaigns against the Liao Tartars and southern rebels, making invaluable contributions. During the Fang La campaign, Bao Xu and Li Kui were assigned to attack the northern gate of Hangzhou. Bao Xu killed the enemy leader Lian Ming and charged into the city. Unfortunately, Bao Xu was sliced into two by Shi Bao who had been lying in ambush inside the city.