Abstract: Against the backdrop of rapid urbanization, the increasingly pronounced urban heat island (UHI) effect has emerged as an ecological challenge attracting wide attention. A deep investigation into the spatiotemporal evolution patterns of the UHI effect is crucial to optimizing urban functional layouts, improving the quality of the living environment, and driving the low-carbon, sustainable development of cities. This study established a UHI intensity dataset based on 1984—2024 temperature data derived from remote sensing. Using this dataset and integrating the Sen-MK trend test, Hurst exponent, and spatial autocorrelation, this study systematically characterized the spatiotemporal evolution patterns of the UHI effect in Beijing's main urban area over the past four decades. The results indicate that the UHI effect in Beijing's main urban area presented a ring-shaped distribution pattern characterized by higher temperatures in the center and lower temperatures at the periphery. The UHI effect showed an evolutionary trend of weakening in the center, intensifying at the periphery, and remaining stable in general. Meanwhile, the UHI effect followed an overall distribution pattern of clustering at the core, fragmentation, and re-clustering sequentially. Specifically, high-temperature and low-temperature areas were concentrated in the center and northwestern ecological conservation zone of the main urban area, respectively. In contrast, the transition zone between the two areas was scattered along the urban expansion edges. Temporally, the UHI effect in Beijing's main urban area generally followed an evolutionary trend of consolidation at the core, differentiation, and ecological mitigation. The main urban area experienced cumulative warming at the periphery and alternating warming and cooling in the center, with oscillatory variations in the UHI effect occurring locally. The results of this study provide a scientific basis for identifying the long-term evolutionary patterns of the UHI effect in Beijing while also offering a reference for space planning optimization, energy conservation and emission reduction, climate adaptation, and ecological governance in the urban area of Beijing.