He became the fifth Chinese player to win a ranking title, following Ding Junhui, Liang Wenbo, Yan Bingtao, and Zhao Xintong.

[3] In July 2017, Fan won five out of the last six frames to beat top seed Luo Honghao 7–6 and win the IBSF World Under-21 Snooker Championship at the tournament held in China.

[4][5] He competed at the 2018 World Snooker Team Cup representing China with Zhang Jiankang but they lost to India 2–3 in the Round of 16.

His first match was a 4–1 loss to Jack Lisowski in the Riga Masters, and his first win was against his practice partner Lyu Haotian 6–5 in the International Championship.

Fan played in the 2019 China National Championship in Xi'an, seeded number 3, but lost in the 3rd round to Jin Long 4–2.

Fan Zhengyi was one of only 4 Chinese players to stay in the UK, but was unable to practice due to lockdown restrictions.

After O'Sullivan missed a long red in the decider, Fan made a 92 break to win the match 10–9 for his first ranking title.

Fan became the fifth Chinese player to win a ranking event, after Ding Junhui, Liang Wenbo, Yan, and Zhao Xintong.

[10] In April 2023 Zhengyi defeated Stephen Maguire in the final qualifying round 10-6 to reach the World Snooker Championship, held at the Crucible Theatre, Sheffield for the first time.

At the invitational Shanghai Masters, he recorded victories over Gary Wilson and Mark Allen, before losing 6–1 in the quarter-finals to Neil Robertson.

[13] His best ranking performances over the rest of the season were quarter-final appearances at the British Open and the German Masters (losing 5–1 to Mark Williams and 5–0 to Kyren Wilson respectively).

[17] At the 2024 English Open in Brentwood in September 2024, he made the first maximum break of his career in the final frame of his 4‍–‍2 win over Liam Pullen.

He nearly achieved this in the World Championship against Zak Surety, but missed a difficult 13th red to a baulk pocket with the remaining balls in good positions.