Mao Jianqing started his professional football career in 2004 with Shanghai Shenhua after graduating from their youth team. In his first season for Shanghai Shenhua he played in four league games, however he would not score his first goal and establish himself for Shanghai until the 2006 season where he was a significant part of the team that came second in the Chinese Super League. The following seasons saw his speed, strength, confidence, strong shot and intelligent ball control make him one not only the club's first choice winger but also the national team, until his public assault charge saw him dropped from the team. While he would regain his place within the team he would still be loaned out to Shenzhen Asia Travel and then eventually a permanent transfer to Shaanxi Chanba on 12 February 2010. He was loaned out to Hangzhou Greentown and later transferred to Beijing Guoan in 2012. He was loan to Shanghai Shenxin in July 2013. In February 2014, Mao was loaned to Qingdao Jonoon until the end of 2014 season.
His strength, speed and effective wing play saw him called up to the under-23 squad to play Football at the 2006 Asian Games in Doha, however he missed the tournament due to injury. Mao Jianqing would still go on to join the senior team and made his debut against Palestine in a 2-0 win on October 11, 2006 where he also scored to send them to the China to the 2007 AFC Asian Cup finals. Under the Head coach Zhu Guanghu he became a highly rated prospect within the Chinese team and started as their first choice left-winger within the Asian Cup Cup tournament. Within that campaign he started in all of China's games where they were knocked out in the group stages and scored his only goal of the tournament against Iran in their 2-2 draw.
In December 2008 Mao Jianqing was arrested for his involvement in a bloody restaurant brawl in the city where a local man was beaten and two women were hurt. The fight started in an apparent fit of jealousy over a woman and came hours after Shanghai Shenhua team suffered a disappointing tie that cost them the league title. After being held in custody for one week and a public apology, Mao was allowed to return to Shanghai Shenhua.