He hailed from Shanyang 山陽 (modern Yanzhou 兖州, Shandong) and came from a poor family. On his search for an appointment in the capital Chang'an 長安 (modern Xi'an 西安, Shaanxi) he became acquainted with Zhang Bo 張勃, who recommended him to the throne. Yet Chen was put into jail because he did not observe the funeral of his father. He nevertheless later managed to become assistant commander (fuxiaowei 副校尉) in the protectorate of the Western Territories 西域, where he proved to he a couraged and witful person.
At the time the Xiongnu 匈奴 khan Zhizhi 郅支 attacked the Wusun 烏孫 and Dayuan 大宛 that were allied with the Han empire. In 36 BCE Cheng Tang was entrusted with a high position in the general staff of Protector-general (duhu 都護) Gan Yannian. The Chinese army heavily defeated the khan and massacred his army.
When Chen Tang came back to the court, Emperor Yuan 漢元帝 (r. 49-33 BCE) decided to reward him with the title of marquis (hou 侯), yet the director of the Imperial Secretariat (zhongshuling 中書令), Shi Xian 石顯, intervened with the argument that Chen Tang was greedy for power. Yet the Emperor finally bestowed him the lowest title of nobility, that of Marquis within the passes (guanneihou 關內侯) and appointed him commandant of the bowmen shooters by sound (shesheng xiaowei 射聲校尉).
When Emperor Cheng 漢成帝 (r. 33-7 BCE) mounted the throne, Counsellor-in-chief (chengxiang 丞相) Kuang Heng 匡衡 accused him of embezzlement of funds sent by the king of the Kangju 康居. He was only spared the death penalty by Gu Yongshu's 谷永疏 advocacy.
In 29 BCE Duan Huizong 段會宗, protector-general of the Western Territories, was besieged by an army of the Wusun. At the court, nobody was able to devise a strategy, only Chen Tang knew a plan to rescue the Chinese troops and was recommended by the powerful general Wang Feng 王風 to be hired again.