Abstract: OBJECTIVE To investigate the prevalence trends and influencing factors for HIV infection complicated with syphilis infection so as to provide bases for development of prevention strategies for dual infections. METHODS A retrospective analysis was performed on the medical records of 328 HIV-infected individuals who were identified at Shanghai Pudong New Area People's Hospital from Jan. 2007 to Dec. 2024. The Joinpoint regression model was applied to analyze the temporal trend of the incidence of coinfection with syphilis, the average annual percentage change (AAPC) was calculated. Multivariate logistic regression analysis was performed for the influencing factors. RESULTS Among the 328 HIV-infected individuals, 123 were co-infected with syphilis, yielding a co-infection rate of 37.50%. Joinpoint regression analysis revealed that the co-infection rate significantly increased at an average annual rate of 5.326% from 2007 to 2024 (AAPC 95%CI: 4.193% to 7.232%, P＜0.001). The year of 2016 was a turning point: a rapid increase occurred from 2007 to 2016 (APC=8.105%, 95%CI: 4.761% to 11.549%, P=0.001), followed by a slower but sustained increasing trend after 2016 (APC=3.874%, 95%CI: 1.892% to 5.856%, P=0.003). Stratified analysis showed that men who have sex with men (MSM) accounted for 78.86% of the co-infected cases, and their infection rate showed a continuous upward trend (AAPC=5.095%, 95%CI: 0.821% to 9.757%, P=0.022). In contrast, no statistically significant change was observed in the infection rate among heterosexuals (AAPC=-3.883%, 95%CI: -11.223% to 3.411%, P=0.334). Multivariate analysis showed that MSM was an independent risk factor for the coinfection (OR=2.229, P=0.006). Attending the dermatology department was a significant pathway marker for identifying the high-risk populations (OR=3.768, P=0.026), while undergoing active testing based on a history of high-risk behaviors was a key protective behavior (OR=0.194, P=0.007). CONCLUSIONS The rate of syphilis co-infection is high and continues to rise among the HIV-infected individuals in the hospital setting, and MSM is the core high-risk population. It is recommended to establish an enhanced screening mechanism by using dermatology departments as sentinel sites, implement comprehensive interventions targeting the MSM population, and promote active testing to control the spread of dual infections.