China's transition from a Soviet-style socialist economy (where there wasn't much space to be corrupt, and in which Mao tried using the Cultural Revolution to create an atmosphere of continuous revolution to purge any inklings of corruption) to a socialist market economy created avenues for government officials to make corrupt earnings. For a time, the CPC tolerated a base level of corruption in exchange for quickly facilitating industrial development and investment from the West (e.g. a government official works faster when bribed than when not, and foreign companies are generally used to bribing because that's what they always do).

Over time however, this kind of corruption invites anti-government sentiment, allows bourgeois ideas to permeate government officials, and could lead to Soviet-style collapse where the corrupt officials decide they want to become the new bourgeoisie. Once China's economic growth slowed down a bit, the cost of bribes also became more of a drain on development.

This is why Xi Jinping began a massive anti-corruption campaign in 2012 and initiated reforms of China’s anti-corruption state institutions. This campaign was originally led by the Supreme People's Procuratorate (China's national prosecutorial agency), which silently collected evidence on corrupt officials until evidence against them was overwhelming and they could be thrown in jail.

To see how they operate, you can watch the TV series In the Name of the People ( English subtitles here; https://www.youtube.com/playlist?list=PLJpCdaWK6PVpeWbeUSjw4dBWt5IKK5Buj ). The series shows how prosecutors work to combat corruption in a fictional provincial government, and was officially funded by the Supreme People's Procuratorate so the Chinese public could understand how fighting corruption worked. You'll notice that the officials who report corruption will get lighter sentences if they themselves are corrupt, or even advance if they themselves are clean.

In 2018, China transferred the task of investigating corruption to a new department, the National Supervisory Commission (国家监察委员会), which has broader powers to investigate corruption within both the government as well as the Communist Party via its co-located sister agency, the Central Commission for Discipline Inspection (中国共产党中央纪律检查委员会). This lets China attack corruption at the state and party level.

Ultimately, corruption is a result of the incentives that exist for government officials. Only by changing these incentives can you remove the possibility of corruption. For example, a dirt-poor state will never be able to stop corruption, because even the government officials will be desperate to get money. Corruption will also flourish if officials are not punished severely (e.g. by firing squad) for it. Fighting corruption must also be seen as a viable pathway for career advancement to incentivize officials to snitch on others' corruption.

China is building a base level of wealth to make corruption unnecessary, anti-corruption prosecutorial institutions to make corruption dangerous, and an atmosphere that combatting corruption is good for one's career (so officials snitch on others' corruption) so that corruption becomes impossible.