As the climate change, the increasing frequency and intensity of extreme climate events have intensified the outbreaks and expansion of cyanobacterial blooms in shallow eutrophic lakes, posing severe threats to lake ecosystem security and water supply safety. However, how extreme climate events drive the long-term dynamics of cyanobacterial blooms and what the dominant factors and mechanisms are remain unclear. Taking Lake Hongze as a case study, a Mann-Kendall trend analysis based on 64 years of meteorological observations revealed that the frequency of extreme high-temperature events has increased significantly at a rate of 2% per decade. Since 1991, the cumulative duration of such events has risen by 5.33 days per decade, and their occurrence frequency has increased by 2 events per decade. Meanwhile, the intensity of extreme precipitation (SDII) and the total amount of very heavy precipitation (R99p) increased by 0.38 mm and 6.88 mm per decade, respectively. Based on remote-sensing observations from 2003 to 2020, the bloom occurrence rate (BO) in Lake Hongze increased by 1.15%, while the maximum bloom extent (MBE) expanded by 154.69 km2. The bloom onset advanced by 24.56 days, and the potential bloom duration (POP) extended by an average of 27.20 days. Further attribution analysis using the SHAP method indicated that BO and MBE were the most sensitive bloom indicators in response to extreme climate events, with the mean intensity of extreme heat events playing a dominant role. The continued intensification of extreme heat events is expected to further advance bloom onset and expand bloom extent. Notably, when temperatures exceed a certain threshold, algal growth may be inhibited due to thermal stress, suggesting a dual “ promoting-inhibiting” effect of extreme heat events on bloom dynamics. This study elucidates the response mechanisms and threshold behaviors of cyanobacterial blooms under extreme climate forcing, providing a theoretical foundation and scientific support for early warning of bloom risks and adaptive watershed management.