Early in the "Kaiyuan" era (713-741) of Emperor Xuanzong, Yuwen Rong served as the treasurer for Fuping County (富平, in modern Weinan, Shaanxi), which was then part of Jingzhao Municipality (i.e., the municipality encompassing Chang'an), and was said to be capable in that capacity. While the officials Yuan Qianyao and Meng Wen (孟溫) successively served as the mayors of Jingzhao, both of them respected his abilities. He later served as "Jiancha Yushi" (監察御史), an imperial censor. At that time, there were many people who tried to evade labor conscription and taxes by avoiding being enrolled on census rolls, or fraudulently claiming exemptions, causing a drain on the imperial treasury. In 721, Yuwen requested that he be specially commissioned to go after census evaders and fraudulent exemption claimers, and, with support from Yuan, who was then a chancellor, Emperor Xuanzong agreed. Yuwen was able to locate some 800,000 alleged census evaders—although traditional historians believed that this figure was inflated—adding much to the imperial treasury. When the county magistrate Huangfu Jing (皇甫憬) submitted a petition arguing that this was causing a panic among the people, Emperor Xuanzong moved Huangfu to a more distant county as punishment. When the deputy minister of census Yang Yang (楊暘) also pointed this out, Yang was sent out of the capital. Subsequently, apparently at Yuwen's urging, Emperor Xuanzong issued an amnesty period for the census evaders to report themselves and allowed them to be exempted from retroactive taxation. When Yuwen toured the realm to announce this, the census evaders, not realizing his earlier role in investigations into them, were exceedingly thankful to him. For his role in the project, Yuwen was promoted to be the deputy imperial censor (御史中丞, "Yushi Zhongcheng").