She represented China at the 2004 Athens Olympics, reaching the top eight in the 5000 m and 10,000 m finals, and set a national record to win the gold at the 2004 IAAF World Half Marathon Championships. The following year Sun ran at the 2005 World Championships and won the Beijing Marathon for a second time. Two days after her win, she won a silver medal at the 2005 National Games of China, but failed a drug test. A former training partner confessed in court to spiking her drink with androsterone, but she still received a two-year ban from the sport. She returned to competition in 2008 but was far from her best form and did not qualify for the 2008 Summer Olympics.