In 582, at age 11, Yang Jun was appointed governor of Luo Province (洛州, roughly modern Luoyang, Henan) and was nominally designated as the commander of the armed forces east of the Hangu Pass.
In 586, Yang Jun was appointed as the regional executive for the provinces south of the Qinling Mountains, stationed in Xiangyang (襄陽, in modern Xiangfan, Hubei).
In 588, when Emperor Wen launched a major campaign against the rival Chen dynasty, Yang Jun was stationed at Hankou (漢口, in modern Wuhan, Hubei) and appointed commander of Sui forces in the central Yangtze River region.
Sui generals Xue Zhou (薛冑) and Liu Ren'en (劉仁恩) defeated and captured Chen Shushen, delivering him to Yang Jun, who subsequently executed him.
In a report to Emperor Wen, Yang Jun expressed humility, stating, "It is unfortunate that I am given even the task of grinding grains, as I contributed nothing to the war effort, and am ashamed of it."
While at Bing Province, Yang Jun began to lead a life of luxury, even building palaces that exceeded what was considered appropriate for an imperial prince.
Upon learning of Yang Jun’s excessive spending and lavish lifestyle, Emperor Wen, who valued frugality, was displeased with his son’s wastefulness.
Only when Yang Jun was close to death did Emperor Wen confer upon him the honorific title of Shang Zhuguo (上柱國), which, in the Sui dynasty's nine-rank system, was first rank, second class, but carried no actual authority.
When Yang Jun's staff requested permission to erect a stone monument in his honor, Emperor Wen responded:[5] For a person to earn a good name, only a few pages in a history book are sufficient.