In December 755, An Lushan and Shi Siming rebelled under the name of removing Yang Guozhong. The ill-prepared Tang government troops retreated with little resistance from all the prefectures in Heshuo () area (which includes the present day provinces of Shandong, Hebei and Henan); only Yan Zhenqing's Pingyuan sustained through. He then combined force with his cousin, Yan Gaoqing (), who was the governor of Changshan () (present day Quyang, Hebei), fighting the rebels at their rear. The government in its desperation, promoted Yan Zhenqing to Deputy Minister of Finance (), and conferred him great military power to assist General Li Guangbi () in the suppression of the rebellion.