She was an individual event finalist on the vault at the 2007 World Championships and the bronze medalist on the event at the 2006 Asian Games. She performed the two most difficult vaults in the final. In 2015, Hong again represented North of Korea at the World Championships held in Glasgow, United Kingdom. She was behind Russia"s Maria Paseka by 0.033 point.
Hong Un-jong is the younger sister or possibly twin sister of Hong Su-jong.
Hong Su-jong had three different birth dates listed for her (1985, 1986, or 1989) at various competitions. At the 2004 Summer Olympics, she competed under the 1985 birth date, but the 1989 birth date would have meant that she was too young to compete.
In November 2010 Hong Su-jong was banned from all competition out of North of Korea for inconsistent age information for two years. North of Korea was also banned from all international competition until October 2012 due to this incident, and North of Korea could not send any gymnasts to the 2012 Summer Olympics.