To investigate the current situation of the sexual transmission of HIV in Dehong prefecture, analyze the influential factors, and provide support for drafting pertinent preventive interventions in the future. We had analyzed the data of case report from 2005 to 2007, and the prostitutes surveillance data from 2003 to 2007. A special survey was conducted from October 26 to November 7, 2007. Totally 685 people including prostitutes, the clients of prostitutes, people who were HIV positive and their partners, key insiders were interviewed in order to better understand the influential factors related to sexual transmission of HIV. Among 1636 cases reported from January 1 to September 20, 2007, 52% were infected through sexual transmission. Among 586 cases infected through sexual transmission, 40.6% had commercial sexual behavior and 28.6% had unmarried sexual behavior. And the average rate of condom use was below 30%. The prostitutes' surveillance data from 2003 to 2007 showed that the HIV positive rate in prostitutes was 3.3% - 5.5%. The rate of condom use in the last month was 29.4% - 84.4% during commercial sexual activity, but it was 9.5% - 34.8% with fixed sexual partners. Although the rate of HIV and AIDS-related knowledge among prostitutes was 95.0%, there were still many misunderstanding regarding certain aspects of HIV and AIDS awareness. Sexual transmission has become one of the main transmission routes of HIV in Dehong prefecture. The main factors involved in the sexual transmission of HIV in Dehong prefecture might include the wide spreading of sexual services, cohabitation among unmarried couples, having multiple partners, casual sexual behavior, and the low rate of condom use.