Introduction: HIV among men who have sex with men (MSM) is a serious global public health concern. The majority of MSM has regular sex partners (MSMRP), and nearly half of those MSMRP have concurrent multiple male sex partnership (CMMSP) in mainland China. Despite of the existing evidence on the risk of spread of HIV heightened by CMMSP among MSMRP, little is known about risk or protective factors of their CMMSP. Based on the theory of planned behaviour (TPB), we examined four cognitive factors (i.e., attitude toward CMMSP, injunctive/descriptive norms against CMMSP, and perceived behavioural control of refraining oneself from CMMSP) of self-reported CMMSP in the past three months among MSMRP. Methods: A cross-sectional study was conducted in Beijing in 2014 and successfully recruited 251 18- to 60-year-old Chinese MSMRP via multiple means, including outreaching in gay venues, online advertisement, and participants’ referrals. Anonymous individual interviews with a structured questionnaire by fieldworkers were conducted in an NGO with privacy ensured. No incentive was given to the participants. Logistic regression analyses were conducted to test the association between demographic and cognitive factors and CMMSP. Results: The prevalence of CMMSP was 48.2% in the sample. Demographic factors had no significant effect but all cognitive factors were significantly associated with CMMSP: positive attitude was a risk factor, while negative attitude, injunctive/descriptive norms, and perceived behavioural control are protective factors. Conclusions: The findings supports the application of TPB to explain CMMSP among MSMRP and facilitates the development of corresponding interventions, which are currently absent.