Background The dualistic diagnostic criteria for metabolic syndrome overlooked the severity of metabolic syndrome, and the relationships between the severity of metabolic syndrome and adverse health conditions are poorly characterized. We therefore aimed to investigate the associations of metabolic syndrome severity with incident cardiovascular disease (CVD)/all-cause mortality. Methods A total of 116,772 participants from the Kailuan study were followed up biennially between 2006 and 2018. The severity of metabolic syndrome was evaluated using a continuous metabolic syndrome severity score (MetS score). Cox proportional hazards model was used to examine the association between MetS score and the risk of CVD and all-cause mortality. Restricted cubic spline analyses were performed to explore the dose-response associations. Results We found that the risk of CVD and all-cause mortality increased consistently with the MetS score. In the multivariable-adjusted model, the hazard ratios of CVD and all-cause mortality were 2.05 (95% CI 1.86-2.25) and 1.45 (95% CI 1.35-1.56), respectively, in those subjects>75th percentile compared with those <25th percentile. Additionally, a J-shaped dose-response relationship was found between MetS score and the risk of all-cause mortality (p(nonlinearity) <.001), while a linear relationship between MetS score and the risk of CVD was observed in this study (p(nonlinearity) = .737). Conclusions This study suggests significant dose-response relationships between MetS score and the risk of CVD/mortality. Subjects without metabolic syndrome but with a relatively high MetS score should raise their awareness and pay more attention to the possible increased risk of CVD events.