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Dietary methylmercury (MeHg) exposure has posed substantial risks to human health. Existing studies have characterized the spatial patterns of China's MeHg exposure. However, the spatial difference and relevant influencing factors have not been investigated. This study quantified the spatial differences of dietary MeHg exposure in China and revealed the relevant influencing factors, which can help optimize the dietary behavior to reduce MeHg exposure. Results show that dietary MeHg exposure in coastal regions is significantly higher than the national average, especially in Shanghai (+191%). Dietary structure difference is the most significant factor influencing spatial differences in MeHg exposure, and its contribution increased from 64% to 73% between 2004 and 2019. In particular, the high proportion of marine fish intake dominates the significantly higher MeHg exposure in most regions. An intake ratio of 2:3 for marine and freshwater fishes is recommended to ensure minimal MeHg exposure and meanwhile meet the nutritional needs. Moreover, narrowing regional dietary behavior disparities can reduce the overall MeHg exposure in China. These findings highlight the importance of region-specific measures in reducing dietary MeHg exposure and implementing the Minamata Convention on Mercury. • Dietary MeHg exposure in coastal regions is higher than the national average of China. • Dietary structure contributes about 70% to the spatial difference in MeHg exposure. • An intake ratio of 2:3 for marine and freshwater fish is recommended for minimal exposure. • Narrowing dietary behavior disparities can reduce the overall MeHg exposure in China. [ABSTRACT FROM AUTHOR]