In 620 AD, in July of the third year of Tang Wude, Li Shimin, the second son of Li Yuan, the founding emperor of the Tang Dynasty, was ordered by his father to go east to Luoyang. This battle was of great significance to the Li dynasty. At this time, the Tang Dynasty had already occupied the Guanzhong region, and was in a strong position with Wang Shichong of Luoyang, Henan, Dou Jiande of Hebei, and Xiao Milling in the south.
Li Shimin led his younger brother Li Yuanji, the king of Qi, all the way to Luoyang, and set up a Tang army camp in Beibi Mountain, north of Luoyang City. Wang Shichong in Luoyang City knew that his troops were not opponents against Li Shimin, and he was ready to wait for the Tang army to run out of food and grass before waiting to attack the Tang army. After months of siege without victory, even Li Yuan, who was far away in Chang'an, couldn't help but be a little worried. Because at this time, part of Tang's main army was besieging Luoyang, and the other part was sent to the south to attack Xiao Mill, and the Guanzhong area was very empty. Once Dou Jiande of Hebei or the Eighteen Divisions of the Grassland raided Chang'an, the army besieging Luoyang had to come to the rescue. The tide of war would take a turn for the worse.
Li Shimin's subordinates thought that the Tang army would not win the war, and fled from the Tang camp without permission. When Li Yuanji heard about this, he humiliated his friend General Chi Jingde and imprisoned him for rebellion.