After graduating from law school, Cheng became a member of the
Democratic Progressive Party (DPP), serving in the
National Assembly as a representative from Taipei from 1996 to 2000 and in the party's youth organization afterwards. She was suspended and resigned from the party in 2002 following a dispute with the DPP leadership over the handling of the sexual harassment allegations against
Twu Shiing-jer. Cheng left the Legislative Yuan following her departure from the DPP, but rumors that she now was aligned with the
Pan-Blue Coalition were confirmed by her appearance at a March 2004 Kuomintang rally protesting the
2004 presidential election. Following her failed campaign to be elected as an independent candidate for
Kaohsiung, she officially joined the Kuomintang (KMT) in 2005. She accompanied Kuomintang chairman
Lien Chan's
visit to mainland China in that year. She was quickly promoted within the party, and was elected as a party-list member of the Legislative Yuan in 2008. She was not reelected upon her run for a Taichung seat 2012, losing to
Ho Hsin-chun. After her defeat, she served as Spokesperson of the
Executive Yuan for two years, being replaced by
Sun Lih-chyun. From her departure from the Executive Yuan to September 2015, she hosted a talk show on
TVBS. She served as deputy secretary-general of the KMT between August and November 2018. She returned to the Legislative Yuan in 2020 and served as secretary-general of the KMT caucus in the Yuan in 2021. On October 12, 2021, she had a heated argument with DPP legislator
Su Tseng-chang regarding the 2002 "ear-licking" case. She left the Yuan at the conclusion of her term in February 2024. On June 11, 2025, Cheng,
Julian Kuo,
Chen Pei-jer,
Holger Chen, and others announced the foundation of the "Opposition Alliance", a party intended to "revive the spirit" of the
tangwai movement and combat the DPP's so-called "
Green Terror". == Chairperson of the Kuomintang ==