Emperor Xuan of Northern Zhou - As Crown Prince

As Crown Prince

Emperor Wu often sent Yuwen Yun on tours of the provinces—and when he himself would go on tours of the provinces or go on military campaigns, he would have Yuwen Yun guard the capital Chang'an.

In 573, Yuwen Yun married Yang Lihua, the daughter of the general Yang Jian the Duke of Sui, as his wife and crown princess.

It was around this time that it came to Emperor Wu's attention that most of Yuwen Yong's associates were men of low character. At the suggestion of the superintendent of the crown prince's palace, Yuwen Xiaobo (宇文孝伯), Emperor Wu made Yuchi Yun (尉遲運), the well-regarded nephew of the general Yuchi Jiong (a cousin of Emperor Wu's), Yuwen Xiaobo's deputy. He also chose a number of men whose characters he had high regard for to serve in other posts as the crown prince's assistance—but Yuwen Yun resented these personnel changes.

In 574, when Emperor Wu's mother Empress Dowager Chinu died, Emperor Wu observed a mourning period for her, and during that period, Yuwen Yun served as regent.

In spring 576, Emperor Wu sent Yuwen Yun on a campaign against Tuyuhun as its nominal commander, but put Yuwen Xiaobo and Wang Gui (王軌) in actual command of the army. In fall 576, the army completed its campaign against Tuyuhun after reaching Tuyuhun's capital Fuqi (伏俟, in modern Haixi Mongol and Tibetan Autonomous Prefecture, Qinghai). Upon return to Chang'an, Wang Gui reported to Emperor Wu that Yuwen Yun and his trusted associates Zheng Yi (鄭譯) and Wang Duan (王端) had committed many immoral activities together. In anger, Emperor Wu battered Yuwen Yun and Zheng with a baton and removed Zheng from his post. Soon, however, Yuwen Yun reinstated Zheng to his post.

Historians also noted that Emperor Wu was very strict with the crown prince, treating him no easier than he did the officials. When he heard that Yuwen Yun liked drinking, he issued an edict forbidding any alcohol from entering the crown prince's palace, and whenever the crown prince had faults, he would whip or batter the crown prince, warning him, "Do you not know how many crown princes had been deposed in history? Is it that my other sons are unworthy of being crown prince?" He also ordered the officials at the crown prince's palace to watch the crown prince closely and submit reports on his actions. In reaction, Yuwen Yun suppressed his own behavior and pretended to have learned his lesson. Nevertheless, Wang Gui repeatedly suggested that Emperor Wu find a better heir, but Emperor Wu declined, because he believed his second son, Yuwen Zan (宇文贊) the Prince of Han to be even less competent than Yuwen Yun, and the other sons to be too young to be considered.

In 577, Emperor Wu destroyed rival Northern Qi, seizing its territory. In summer 578, however, he grew ill suddenly while preparing a campaign against Tujue, and he, after entrusting the important matters to Yuwen Xiaobo, died. Yuwen Yun took the throne as Emperor Xuan.