It was said that Lu Xisheng was studious and was good at writing. He particularly understood the I Ching, the Spring and Autumn Annals, and the Tao Te Ching well, and wrote many commentaries. At one point, he served on the staff of Zheng Yu (鄭愚) the prefect of Shang Prefecture (商州, in modern Shangluo, Shaanxi), at Zheng's request. After he left his service under Zheng, he became a hermit in Yixing. After a long period of time, he was summoned by the imperial government to serve as You Shiyi (右拾遺), an advisory official at the legislative bureau of government (中書省, Zhongshu Sheng). It was said that at that time the ruling officials were corrupt, and there had been several years of bad harvests, with the situation being particularly severe in the region of Bian (汴州, in modern Kaifeng, Henan) and Song (宋州, in modern Shangqiu, Henan) Prefectures. Lu realized the severity of the situation and submitted petitions that warned that these conditions would be prime for the appearance of agrarian rebels, but apparently his petition drew no reactions. The next year, as he warned, the agrarian rebel Wang Xianzhi started a major rebellion. Lu later served as the prefect of She Prefecture (歙州, in modern Huangshan, Anhui). Emperor Zhaozong heard of his fame, and recalled him to the imperial government to serve as imperial attendant (給事中, Jishizhong).