The mpox outbreak since 2022 had attacked the community of men who have sex with men (MSM) heavily. This large cross-sectional study investigated the levels and associated factors of mpox risk perception among young MSM (YMSM) aged 18-29 years in six provincial regions of China in September 2022. The participants were recruited via facility-based sampling. Mpox risk perception was measured by perceived susceptibility and perceived severity of mpox. Geodetector was used to measure stratified heterogeneity of mpox risk perception. Univariate and multivariable linear regressions were used to examine the factors associated with mpox risk perception. A total of 2493 participants were included with a mean age of 24.6 years. The proportion of perceiving a susceptibility of mpox under different scenarios ranged 3.7%-17.0% and that of perceiving a severity of mpox ranged 81.6%-83.2%. Stratified heterogeneity of perceived susceptibility, perceived severity, and overall perceived risk of mpox were observed in several characteristics such as study sites, monthly income, risk behaviors, and psychosocial factors. Multivariable regression showed the level of mpox risk perception was positively associated with having in-person gathering activities (b  = 0.457, 95% CI: 0.208, 0.705), history of HIV infection (b  = 0.431, 95% CI: 0.028, 0.834), depressive symptoms (b  = 0.069, 95% CI: 0.049, 0.090), and self-stigma to MSM identity (b  = 0.047, 95% CI: 0.024, 0.071). The Chinese YMSM showed a high level of perceived severity of mpox but a low level of perceived susceptibility. It is warranted to strengthen targeted risk communication of mpox, develop comprehensive and unstigmatized health messages, and provide mental health support for YMSM.