Xu Si first started playing snooker aged 12 at his local club in Jieyang during the school holidays.

[1] Prior to turning professional, Xu began playing in minor-ranking Asian Players Tour Championship from age 15, and his first appearance at a ranking event was in the wildcard round of the 2014 Shanghai Masters where he was whitewashed 5-0 by Ryan Day.

[2] He also made a wildcard appearance at the 2016 World Open where he defeated veteran James Wattana 5-3 or progress to the last 64, where he lost in the next round against Daniel Wells.

He then won two matches at the 2016 International Championship, defeating professionals Wang Yuchen at the wildcard stage, and two-time world champion Mark Williams in the last 64 before losing to Wattana in the last 32.

However, in only his third tournament, the 2017 Indian Open, he beat Michael Georgiou, Robin Hull, Sean O'Sullivan, Ricky Walden and Dave Gilbert to reach the semi-final, where he lost to John Higgins 4–2.

His best win was a highly emotional match against Martin Gould in the China Championship qualifying round, which he won 5–4 on the final black.

Xu Si came through the first event of the 2019 Q School by winning five matches to earn a two-year card on the World Snooker Tour for the 2019–20 and 2020–21 seasons.

In World Championship qualification, Xu needed to win his first match to renew his professional tour card via the 1-year ranking list.