Background Unprotected anal intercourse (UAI) is a major pathway towards secondary HIV transmission among men who have sex with men (MSM).We explored the socio-cultural environment and individual beliefs and experiences conducive to UAI in the context of Southern China. Methods We employed an ethnographic approach utilizing a socio-ecological framework to conduct repeated in-depth interviews with thirty one newly diagnosed HIV positive MSM as well as participant observations in Shenzhen based healthcare settings, MSM venues and NGO offices. Results Some men (6/31) reported continuing to practice UAI after an initial diagnosis of being HIV positive. For MSM who had existing lovers or stable partners, the fear of losing partners in a context of non-serostatus disclosure was testified to be a major concern. MSM with casual partners reported that anonymous sexual encounters and moral judgments played a significant role in their sexual risk behaviors. Simultaneously, self-reported negative emotional and psychological status, perception and idiosyncratic risk interpretation, as well as substance abuse informed the intrapersonal context for UAI. Conclusion UAI among these HIV positive MSM was embedded in an intrapersonal context, related to partner type, shaped by anonymous sexual encounters, psychological status, and moral judgments. It is important that prevention and intervention for secondary HIV transmission among newly diagnosed HIV positive MSM in China take into account these contextual factors.