Sun Jun started his professional football career in 2012 when he was promoted to Yanbian FC's first team squad.
[1] He would soon go on to establish himself as an integral member within the team and win the 2015 China League One division title as well as promotion to the top tier at the end of the campaign.
[2] On 5 March 2016, Sun made his Chinese Super League debut in the first match of 2016 season against Shanghai Shenhua, in a game that ended in a 1-1 draw.
After an unsuccessful promotion push at the end of the season on 26 February 2019, Yanbian FC was dissolved due to financial difficulties from owing taxes.
[8] Often used sparingly he would go on to be loaned out to Xi'an Daxing Chongde and then Hebei Zhuoao before joining second tier club Shanghai Jiading Huilong.