Objective This study aimed to determine the independent and joint associations of sedentary time (ST) and physical activity (PA) with metabolic syndrome (MetS) and its components among Chinese adults. Methods The study analyzed data from 4,865 adults aged ≥ 18 years who participated in the 2009 and 2015 China Health and Nutrition Surveys (CHNS). Four types of leisure ST and three types of PA self-reported at baseline were collected. Multivariable logistic regressions were used to determine the independent and joint associations of ST and PA with the odds of MetS or its components. Results For independent effects, higher levels of television time and total leisure ST was associated with higher MetS risk [odds ratio (OR) 1.3, 95％ confidence interval (CI) 1.1–1.6, P < 0.001; OR 1.4, 95％ CI 1.2–1.8, P 7 hours/week (h/w) group was higher than that in the < 7 h/w group in (OR 1.5, 95％ CI 1.2–1.9). Higher levels of moderate-to-vigorous-intensity physical activity (MVPA) and total PA were associated with a lower MetS risk (OR 0.7, 95％ CI 0.6–0.9, P < 0.001; OR 0.8, 95％ CI 0.7–0.9, P < 0.001, respectively). For the joint effects, compared with those reporting the lowest level of total leisure ST (< 14 h/w) and the most active tertile of MVPA (≥ 61.0 MET-h/w), participants reporting the most total leisure ST (≥ 35 h/w) and the lowest level of MVPA (0 MET-h/w) had the highest odds of MetS (OR 2.0; 95％ CI 1.4–2.7). Except for people reporting ST (14–21 h/w) within the most active tertile of MVPA, the associations in all other groups were significant. With the increase of TV time and decreased MVPA, the odds of MetS almost showed a curve acceleration. Conclusions MVPA and total PA have independent preventive effects, and sedentary behavior (mainly watching TV) has an unsafe effect on MetS and its components. Strengthening the participation of MVPA and combining the LPA to replace the TV-based ST to increase the total PA may be necessary to reduce the prevalence of MetS in Chinese adults.