Global warming has accelerated glacier melt, leading to the increased formation of glacial lakes and heightened flood risk in downstream regions. This study focuses on the Merzbacher Glacier Lake (MGL) to model the hydrodynamics of its downstream area. Utilizing a relationship curve between lake area and water volume for the “lower lake”, we predicted the outburst time, volume, and downstream impact of a potential 2023 MGL outburst flood. Our predictions indicated that a glacial lake outburst flood (GLOF) would occur between July 3rd and 5th, with flood inundation extending approximately from the river’s centerline outwards, affecting some agricultural land in Wensu County, but having minimal impact on urban areas. Satellite imagery monitoring subsequently revealed that the Merzbacher Glacier Lake began to gradually drain after July 3rd, with nearly complete drainage of the lake water by July 8th, leaving only glaciofluvial sediments on the lakebed. The observed outburst time was indeed between July 3rd and July 5th, and the outburst flood volume was approximately 10 million m3. These observational results align well with the predictions of this study, validating the accuracy of the proposed methodology. This approach can be extended to other glacial lake regions, providing valuable early warning support for potential downstream flood inundation risks.