The submission that Su wrote on Pei Judao's behalf was said to be well-written in an intricate manner, and he became famous.
In late 694, Wu Zetian, displeased with the power Li had, exiled Li, and fellow chancellor Zhou Yunyuan and the assistant chief judge of the supreme court, Huangfu Wenbei (皇甫文備), then submitted articles of impeachment against Su and several fellow chancellors – Doulu Qinwang, Wei Juyuan, Du Jingjian, and Lu Yuanfang—for not being able to curb Li Zhaode's power.
However, Su was soon recalled to be deputy minister of civil service affairs (天官侍郎, Tianguan Shilang).
Su, on the other hand, walked to prison, slept on a thin mattress, and ate very simple foods.
Wu Zetian ordered the local government to supply his funeral needs, but Su used this opportunity to take over neighbors' lands and destroy their tombs.
The censor Xiao Zhizhong submitted an article of impeachment, and she demoted Su to be the prefect of Fang Prefecture (坊州, in modern Yan'an, Shaanxi).
He was then made the secretary general at Yi Prefecture (益州, roughly modern Chengdu, Sichuan).