Abstract: Objective To explore the high-risk sexual behavior features and its influencing factors of the human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) cases with extra-marital heterosexual transmission, and to provide basic data for controlling HIV heterosexual transmission. Methods New reported HIV/AIDS cases with extra-marital heterosexual transmission in Yunnan Province in 2015 were recruited. Face to face questionnaire was used to get the information as risk behaviors before and after inform HIV infection. Results A total of 498 males and 490 females were recruited; 39.88% (male 68.67%, female 10.61%) of the cases had business sexual behaviors before informing HIV infection in the near one year, there was significant difference between genders (χ²=352.797,P<0.001).The site centralized in the street sides. Persistent condom using rate was only 8.38%;71.36% (male 64.46%,female 78.37%)had temporary sexual behavior, there was significant difference between genders (χ²=23.379,P<0.001). 82.52% were among the friends/acquaintances. The multiple and cross sexual behavior existed. 12.96% of those informed infected cases still insisted unprotected high risk sexual behaviors. Only 31.86% of them were willing to tell the sexual partners their infection status. Conclusions Heterosexual HIV/AIDS transmission population is enlarging. The strategy should transfer into strengthen high-risk population intervention, and advocate universal condom use. Sexual responsibilities, sexual health and sexual safety propaganda should be added as well. The spread risk assessment of the HIV/AIDs in the follow-up management should be included and steps should be taken accordingly.