Two years later, Yuan once again made it to the final, where he defeated Fan Zhengyi 6–2 to win the Asian Under-21 Championship; as a result, he was given a two-year card on the professional World Snooker Tour for the 2017–18 and 2018–19 seasons.

Yuan's first match as a professional was a narrow loss to Oliver Lines in the 2017 Riga Masters qualifiers on 31 May 2017, two days after his 17th birthday.

In the German Masters, he beat 4-time World Champion John Higgins 5–4 on the final black, somewhat controversially as the cue-ball appeared to touch the rest (a foul stroke) after the players had shaken hands.

He beat World Champion Mark Williams 4-3 and Stephen Maguire 4–2 to reach his second quarter-final, losing to flatmate Xiao Guodong 5–4.

Yuan's most notable achievement was reaching the third round of the Northern Ireland Open, beating close friend Luo Honghao and Tom Ford before eventually losing 4–0 to Ding Junhui.

Yuan's best result of 2021-22 was a 3rd round appearance in the European Masters, beating Stuart Carrington and Ricky Walden, before losing to Liang Wenbo.

Yuan Sijun won his first round group, against Barry Hawkins, Ken Doherty and Lei Peifan, without losing a frame.

At the start of the 2018/2019 season, Yuan Sijun moved to Darlington and is based at the Q House Academy, managed by Chusak Phetmalaikul.