Background: Starting from May 31 ^st, 2023, the local transmission of monkeypox (Mpox) in mainland China began in Beijing. Till now, the transmission characteristics have not been explored. Method: Based on the daily Mpox incidence data in the first three weeks of Beijing (from May 31 ^st to June 21 ^st, 2023) , we employed the instant-individual heterogeneity transmission model to simultaneously calculate the effective reproduction number ( R _e) and the degree of heterogeneity ( k) of the Beijing epidemic. We additionally simulated the monthly infection size in Beijing from July to September and compared with the reported data to project subsequent transmission dynamics. Results: We estimated R _e to be 1.68 [95% HPD:1.12, 2.41], and k to be 2.57 [95% HPD: 0.54, 83.88], suggesting the transmission of Mpox in Beijing was supercritical and didn’t have considerable transmission heterogeneity. We projected that R _e fell in the range of 0.95 to 1.0 from July to September, highlighting more efforts needed to further reduce the Mpox transmissibility. Conclusion: Our findings revealed supercritical and homogeneous transmission of the Mpox epidemic in Beijing. Our results may provide reference for understanding and predicting of the on-going Mpox transmission in other regions of China and assess the effect of control measures.