Abstract: Under the influence of global warming, the continuously growing marine heat wave (MHW) has a serious impact on the climate system and social economy, of which the Western Pacific Warm Pool (WPWP) area is a typical area of MHW characteristic changes. Based on the MHW database, the National Centers for Environmental Prediction atmospheric and oceanic reanalysis data, and the chlorophyll a concentration data provided by the National Aeronautics and Space Administration Aqua satellite and the Biogeochemical-Argo floats, we explore the evolution characteristics, physical mechanisms, and ecological impacts of MHW in the WPWP from 2020 to 2022 using statistical methods, such as composite analysis and singular value decomposition. The results showed that MHW properties in the WPWP region have increased significantly in the past 30 years and are closely related to the continuous La Niña events. Under the background of multiyear La Niña events from 2020 to 2022, the frequency of MHW in the WPWP reached the highest in the world, and the coverage area, frequency, total days, and cumulative intensity of MHW have been the most notable since 1982. The mixed layer heat budget equation in the WPWP region shows that the occurrence of the strongest MHW from 2020 to 2022 is mainly dominated by the downward short-wave radiation term in the net flux and the latitudinal advection term in the marine dynamic processes. We also determine that the MHW properties and marine ecological indicator chlorophyll a concentration have a negative correlation on the spatial and temporal scales in the WPWP region, particularly the MHW events from 2020 to 2022 that caused a significant decline in the overall phytoplankton biomass in the upper ocean of the region.