Land surface temperature (LST) serves as a crucial parameter in scientific investigations pertaining to resource management, climate change, and terrestrial ecosystems. The implementation of large-scale water conservancy projects influences the water areas of the water source, thereby affecting regional climate, vegetation, and consequently, the LST. At present, widely used moderate resolution imaging spectroradiometer temperature products often exhibit data loss or distortion due to atmospheric interference or technical challenges. We introduce an advanced interpolation of the mean anomaly method, grounded in the digital elevation model, to address these missing values. Moreover, we utilize indicators such as temperature difference (TD) and project effect change intensity (PECI) to scrutinize the influence of the aforementioned water diversion project on the study area’s LST. Our findings indicate that: (1) The R2 values for the improved interpolation of mean anomalies based on the digital elevation model method for LST reconstruction consistently exceed 0.902, demonstrating higher accuracy in regions with significant elevation differences, especially during nighttime. (2) The TD is correlated with the proximity and size of water bodies. (3) The PECI is notably higher during wet seasons and nighttime. There is a minimal variation in the prevalence of extremely strong impact areas across different periods. (4) Subsequent to the middle route of the South-to-North Water Diversion Project, both warming and cooling effects have been observed in the study area. Notably, the direction of the warming effect is divergent in the northern mountainous regions compared with the central and southern plains.