Baseflow plays a vital role in protecting the environment and ensuring a stable water supply for farming. There are still gaps in the current understanding of baseflow convergence rates in the humid region due to the abundance of rainfall and the high‐water table. Therefore, this study focused on the evolution and hysteresis characteristics of baseflow in humid basins of southeastern China. The baseflow ensemble simulation (BES) method was established to improve the reliability and applicability of baseflow simulation. We suggest a way of differentiating the wet and dry seasons based on the multi‐year average monthly baseflow index (BFI) to determine the intra‐annual distribution of water effectively and simply. The hydrological hysteresis effect of baseflow on precipitation is revealed by characterizing baseflow response to precipitation under precipitation events during wet and dry seasons. A methodology for assessing the performance of baseflow simulation was proposed from observations of streamflow and precipitation. We found that the BES method performed better in baseflow simulation than other single separation methods. Using the BES method, the lag time of baseflow to precipitation during the wet and dry seasons was found to be 3.09 and 4.04 days after utilizing the BFI to divide the hydrological situation into wet and dry seasons. Additionally, precipitation had nearly twice as much intensity influence on baseflow during the dry season compared to the wet season. These findings have significant ramifications for the use, management, and planning of water resources in humid areas of China. Plain Language Summary The importance of researching baseflow in humid places is expanding as drought conditions occur more frequently. The lag time effect of baseflow on precipitation varies spatially and temporally, while the applicability of each baseflow simulation method varies in different regions. In this study, we validated the performance of a baseflow ensemble simulation method in the humid region of southeastern China. Humid regions had a shorter lag between baseflow and precipitation than desert, semiarid, and semi‐humid zones. The lag time of baseflow for rainfall simulated by the BES method was in the middle of the four methods. Additionally, compared to the dry season, the baseflow lag time was noticeably shorter during the wet season. This is because the humid region basin receives most of its yearly precipitation during the rainy season, primarily in the form of intense rainfall that lasts just a brief time. In addition, baseflow variations coincided with variations in precipitation during the rainy season, while there was a delay between variations in baseflow and changes in precipitation during the dry season. Understanding the effects of climate change and water use on groundwater‐surface water interactions in humid regions of China is significantly impacted by these findings. Key Points An ensemble‐based baseflow simulation method is proposed to characterize the uncertainty of each baseflow separation method The hydrologic hysteresis between baseflow and rainfall was found to be within 1 week in the humid basins of Southeastern China The influence of precipitation on baseflow in the humid basins is significantly stronger in the dry season than in the wet season