Incidence rate of cardiovascular disease (CVD) has significant seasonal trend, being higher in winter. However, the extent to which the seasonal variation of CVD deaths was caused by temperature remains unclear. We obtained daily data on temperature and CVD and myocardial infarction (MI) mortality from nine Chinese mega-cities during 2007-2013. Distributed lag non-linear models were applied to assess the city-specific temperature-related daily excess deaths across lag 0-21 days, using the minimum-mortality temperature as reference. Then, estimates of excess deaths in four seasons were separately aggregated from the daily series, and its ratio to the corresponding total deaths produced seasonal attributable fraction (AF). In total, 1,079,622 CVD and 201,897 MI deaths were recorded in the nine Chinese cities. Significant and non-linear associations between temperature and mortality were observed, with a total of 195,516 CVD and 50,658 MI deaths attributable to non-optimum temperatures. 103,439 (95% empirical CI: 54,475-141,537) CVD and 24,613 (5891-36,279) MI deaths related to non-optimum temperature occurred in winter, compared with 15,923 (1436-28,853) and 4946 (-325-9016) in summer. Temperature-related AFs were higher among MI than CVD, with AFs of 42% (9-62%) and 35% (19-48%) in winter, and 13% (-1-23%) and 8% (1-14%) in summer, respectively. This study may have important implications for developing effective targeted intervention measures on CVD events.