Later, he was sent out of Chang'an to serve as the prefect of Hu Prefecture (, in modern Huzhou, Zhejiang). Within his territory was a lake that, during the time of the Southern Dynasties, provided irrigation water for a large area, but which since then had become abandoned. Yu ordered that its reconstruction be carried out, and thereafter, the people received not only the benefits of irrigation but also of fishing. As the prefecture did not have much usable land, many human corpses went unburied, and Yu established more than 10 burial sites for the bodies. He later served as the prefect of Su Prefecture (, in modern Suzhou, Jiangsu), and it was said that the irrigation ditches and the streets that he constructed were still heavily relied upon at the time that the "Old Book of Tang" was written — i.e., during Later Jin. Believing that there were too many odd temples in his territory, he had them destroyed, leaving only the temples of Taibo of Wu and Wu Zixu. However, while Yu was said to be able as a prefect, he was also said to be cruel and unreasonable at times, often caning people, particularly when he was at Hu Prefecture. His superior, the circuit governor (, "Guanchashi") Wang Wei () reported this to then-reigning Emperor Dezong, but Emperor Dezong took no actions against Yu. (After Yu was later promoted several times, he wrote a letter to Wang to brag, "After I received your poor comments, I was promoted three times.") Yu was later promoted to be "Dali Qing" (), the chief judge of the superior court, and yet later served as the governor of Shan'guo Circuit (, headquartered in modern Sanmenxia, Henan). As he believed that he was becoming powerful, he was further abusing his power and being cruel, punishing many of his subordinates daily with heavy punishments. On one occasion, a secretary, Yao Xian (), becoming distressed over Yu's cruelty, jumped into a river (probably Yellow River) to his death while rowing on the river with his brother.