Taking nine major river basins in China as the research objects, seasonal drought and flash drought events from 1981 to 2021 were identified at the grid scale using the standardized evaporation stress ratio and standardized precipitation evapotranspiration index. Based on the nonlinear models, a response relationship model between seasonal drought and flash drought was constructed, and the spatiotemporal response relationship between seasonal drought and flash drought was evaluated. The results indicate that the frequency of flash drought during seasonal drought is significantly higher than that before and after seasonal drought. However, the other flash drought characteristics show little change before and after seasonal drought. The longer duration and higher intensity of flash drought are mainly observed in northwestern China, while the higher drought peak is found in southwestern, northeastern, and eastern China. The spatial changes in seasonal drought characteristics before and after flash drought are relatively small, with higher frequency of seasonal drought occurring in northeastern and southern China, and higher intensity and peak in northwestern China. The response of seasonal drought to flash drought varies greatly in different basins. The high-intensity flash drought in the Southeast Rivers, Yellow River,and Songliao River basins generally triggers high-intensity seasonal drought, while the high-peak flash drought in the Songliao River, Southwest Rivers, and Pearl River basins triggers high-peak seasonal drought.