After training at the Wiraka Billiard Academy in Foshan, he moved to the United Kingdom aged 16 and earned a two-year tour card through the 2019 Q School for the 2019–20 and 2020–21 seasons.

At the 2023 World Snooker Championship, Si won three qualifying matches to reach the tournament's final stages at the Crucible Theatre for the first time.

Although he led 14–5 in the semi-final, he lost 15–17 to the eventual winner Luca Brecel; this nine-frame deficit was the largest lead overturned in the history of the World Championship.

[8] Si spent the 2021–22 season competing as an amateur, but earned top-up places in ranking tournaments through his high placement in the 2021 Q School Order of Merit.

In a BBC radio interview after the match, Murphy objected to amateur players featuring in professional events, saying that he had "lost to someone who shouldn’t even be in the building".

[9] The World Snooker Tour issued a statement disagreeing with these remarks,[10] and Murphy subsequently apologised for "taking the shine off" Si's win.

[12] At the 2022 European Masters, he defeated Anthony McGill and Daniel Wells to reach his first quarter-final at a ranking event, which he lost 2–5 to Kyren Wilson.

[15] Si defeated Robert Milkins 13–7 in the second round and McGill 13–12 in the quarter-finals,[16][17] becoming the first Crucible debutant to reach the World Championship semi-finals since Andy Hicks in 1995 and the youngest player to do so since Ronnie O'Sullivan in 1996.