Later in 396, Northern Wei launched a major attack on Later Yan, quickly taking Bing Province (并州, modern central and northern Shanxi) and then descending on Zhongshan, putting it under siege. In spring 397, after being unable to force Northern Wei to lift its siege and after Murong Bao's brother Murong Lin the Prince of Zhao rebelled, Murong Bao decided to abandon Zhongshan and flee to Longcheng. Murong Sheng followed his father in joining his brother Murong Hui's army, which had advanced south from Longcheng. Later that year, after Murong Hui killed Murong Long and severely wounded another uncle, Murong Nong, in an attempted coup to force Murong Bao to create him crown prince, Murong Hui was defeated and killed. Meanwhile, Murong Sheng became one of the major generals.