Later in Emperor Gaozong's reign, he was made the secretary general at Jing Prefecture (荊州, roughly modern Jingzhou, Hubei).
On an occasion in 682, Emperor Gaozong sent eunuchs to the Yangtze River region to seek out unusual bamboo plants, hoping to transplant them to the imperial garden.
He wrote an edict thanking Su, and ordered that the collected bamboo plants be thrown into the river.
However, while serving at Jing Prefecture, Su was also involved in an embarrassing event that caused people to believe that he did not study well.
As Empress Dowager Wu had taken up permanent residence at the eastern capital Luoyang, Su was made the official in charge of Chang'an; he was also created the Duke of Wen.
Su rejected the proposal, pointing out that it was inappropriate for the imperial government to be competing on the market with farmers.
In 686, Su was recalled to Luoyang to serve as Wenchang Zuo Xiang (文昌左相) -- one of the heads of the executive bureau and also a post for a chancellor—and further given the chancellor designation Tong Fengge Luantai Sanpin (同鳳閣鸞臺三品).
Around this time, there was an incident where he encountered Empress Dowager Wu's lover, the Buddhist monk Huaiyi.
"[2] In spring 690, Su was removed from his post as head of the executive bureau, but was given the honorific title Tejin (特進) and continued to serve as a chancellor de facto with the Tong Fengge Luantai Sanpin designation.