Ou's activism started after convincing her parents, both university lecturers, to adopt several lifestyle choices to reduce their own carbon footprint.[2] In late May 2019, at age 16, she did a school strike for climate by holding up homemade banners for several days in front of City Hall in Guilin to call for immediate stronger action on climate change.[3][4]Greta Thunberg said she is a "true hero", then the authorities said she must stop due to not having a permit.[5][6][7] Her WeChat account was blocked.[8] In September 2019, she organised a "Plant for survival" campaign. With her pocket money, she bought trees and planted them around Guilin.[9] She was not allowed to return to school as long as she engages in climate activism.[10][11][12]
Ou keeps in touch with environmental activist Zhao Jiaxin.[11] After she and three other activists were detained after a silent protest in front of the Shanghai Exhibition Centre in September 2020[16] she was called "incredibly brave" by Greta Thunberg.[17] Ou and her parents have become vegetarians.[2]
In Lausanne, Switzerland, Ou started a hunger strike on Palud Square on 19 April 2021, to protest her 60-day prison and 1,200-Swiss francs fine sentence for protesting against expansion of the exploitation of the limestone quarry on Mormont hill by the Swiss-French cement company LafargeHolcim.[18][19] In 2024, she was fully acquitted by the Supreme Court of Switzerland, which ruled that she had not obstructed police action.[20]