Poyang Lake, the largest freshwater lake in China, played a vital role in regional water supply and flood regulation. In recent years, the lake's surface water area underwent significant changes due to the combined impacts of climate change and human activities. However, traditional remote sensing methods often faced limitations in processing multi-source imagery efficiently, while hindered large-scale and long-term dynamic monitoring. To address this, this study utilized the Google Earth Engine (GEE) platform to integrate multi-source remote sensing, meteorological, and land use data from 1990 to 2024, aiming to systematically analyze the spatiotemporal dynamics of Poyang Lake's surface water area and its driving factors. The results indicated that: (1) On the temporal scale, the annual maximum and minimum water surface areas of Poyang Lake in 2024 decreased by 14.04% and 28.04% respectively compared to 1990, showing significant area variations and notable fluctuations. Seasonally, the water area exhibited greater changes in spring and autumn while remaining relatively stable in summer and winter, with the most pronounced reduction occurring in winter. The overall reduction from 1990 to 2024 reached 927.85km². (2) Spatially, during the wet season, both the main lake body and dish-shaped sub-lakes expanded significantly, showing typical lacustrine characteristics. In the dry season, the lake area contracted and became fragmented, with the water surface retreating most noticeably in the tail reach of the Ganjiang River, overall showing fluvial characteristics. (3) In response to climate change, total precipitation increased by 346.68 mm over the study period, with an average annual growth rate of 9.91mm/a, approximately 16.74% higher than the multi-year average. Precipitation was positively correlated with the surface water area, and its fluctuations significantly influenced lake expansion and contraction. Meanwhile, the annual mean temperature increased by 1.01℃ (0.03 ℃/a on average), with a cumulative rise of 5.57%, showing a strong negative correlation with lake area. Rising temperatures likely intensified evapotranspiration, indirectly contributing to lake shrinkage. (4) Regarding anthropogenic impacts, 533.19km² of lake surface was converted into construction land during the study period, directly compressing the lake area. Additionally, 18339.39km² of forest land was transformed into cropland and built-up areas, weakening the region's water retention and ecological regulation capacity, thereby exacerbating fluctuations in surface water area. The integration of multi-source data and long-term time-series analysis methods on the GEE platform enables efficient, automated monitoring of water-body dynamics, offering a technical framework for studies of other large lakes. Moreover, the findings provide decision-support for lake water-resource management and the formulation of ecological conservation policies.