It is not known when Yang Dongqian was born. His ancestors had been Tang officials, with his great-great-grandfather Yang Hui serving as the governor of Suining Commandery — and thus being datable to the reign of Emperor Xuanzong of Tang, during whose reign, for some time, Tang prefectures were known as commanderies. Yang Dongqian's great-grandfather Yang Mian moved from there south of the Nanling Mountains, to Shixing, and made his home there. Neither Yang Dongqian's grandfather Yang Chui and father Yang Zhen were recorded to be in official service, but both were said to be honest and virtuous. Yang Dongqian himself was said to be studious in his youth, open-minded, and understanding of principles of governance. At one point, he became a surveillance officer for Yong District, then still under Tang Dynasty rule. After the end of his term of service, he went to live in Guang Prefecture.
Service under Liu Yin and Liu Yan prior to Southern Han's founding
At one point, Yang Dongqian was retained to serve on the staff of the warlord Liu Yin, who then controlled the region as the military governor of Qinghai Circuit. Liu Yin honored Yang Dongqian as a teacher for himself, and also had Yang serve as his secretary in his role as military governor of Qinghai and Jianwu Circuits. He was said to be Liu Yin's chief strategist in planning the seizure of Ningyuan Circuit, which eventually happened in 911, from Liu Yin's northern neighbor, Ma Yin the Prince of Chu. In 911, Liu Yin died and was succeeded by his brother Liu Yan. Yang continued to serve Liu Yan, and he suggested to Liu Yan that he should not commission army officers as prefectural prefects. Rather, Yang advocated that he select refugees from the Central Plains who were well-learned, first putting them on his staff to test them and then make them prefects, so that they could govern the prefectures well and benefit the people. Liu Yan agreed. Also in 911, Lu Yanchang, the warlord who controlled the Qian Prefecture region, was killed by his officer Li Qiu, who subsequently died and was succeeded by his officer Li Yantu. At Yang's suggestion, Liu Yan attacked Shao Prefecture, which was then under control of Li. Liu's army defeated the garrison there, and Shao's prefect Liao Shuang fled to Chu, allowing Liu to take over Shao. Yang subsequently also provided strategic opinions that helped Liu to repel the attempts by Ma to retake Ningyuan, allowing Liu to retain the lands of the original five districts originally belonging to Qinghai's predecessor circuit Lingnan Circuit. For Yang's contributions, Liu made him the deputy military governor. After Later Liang's Emperor Taizu sent the emissary Wei Jian to try to intercede in the conflict between his two vassals Liu and Ma in 912, Yang advocated entering into a marital alliance with Ma in order to settle the two realms' differences. Liu agreed, and in 913 asked Ma for permission to marry one of his daughters. Ma agreed.
During Liu Yan's reign
In 917, Liu Yan declared himself emperor of a new state of Yue as its Emperor Gaozu. He was about to name Yang Dongqian a chancellor with the designation Tong Zhongshu Menxia Pingzhangshi and minister of defense, but Yang, believing that he should not be honored above another chancellor candidate, Zhao Guangyi, who had been a Later Liang emissary and whose brother Zhao Guangfeng was a chancellor to Later Liang, offered to be subordinate to Zhao. Liu agreed, and while he named Zhao, Yang, and another Later Liang emissary, Li Yinheng, all as chancellors, Zhao received the greater secondary office of minister of defense, while Yang was given the secondary office of deputy minister of defense. In 920, Yang made the proposal to build schools, to generally teach the people about the proper rites, and to restart imperial examinations that had been a major part of the Tang civil service system. Liu agreed. However, several suggestions that Yang made to Liu fell on deaf years. For example, when Liu built watery prisons to torture prisoners, Yang urged against it, to no avail. Further, around 934, Liu had his oldest son Liu Hongdu the Prince of Qin conscript a group of 1,000 soldiers to serve as his guards, but Liu Hongdu selected many hoodlums who behaved poorly, and became close to them. Yang, finding this situation untenable, went to speak to Liu Yan: However, Liu Yan responded, "This is just for my son to teach them about war. I am sorry this is overly concerning you, Lord." He made no attempts to curb Liu Hongdu's behavior. Once Yang exited the palace, he saw Liu Hongdu's guards robbing gold and silk from merchants, but the merchants did not dare to make reports against them. He lamented and stated, "If the governance has become this troubled, what use is there for a chancellor?" He therefore claimed an illness and returned to his mansion. He was there for quite some time without Liu Yan ever making an attempt to summon him again. He died at home in 935.
