Abstract: Tracking and analyzing the valley deformation of a high dam during construction is of great significance for high slope stability and dam safety. In this paper, the finite difference method is used to simulate the evolution of valley deformation. Based on the engineering environment and geological structure of an extra-high arch dam, we tracked and analysed the monitoring data of rock mass deformation on both sides of the dam area, and discussed the driving factors and evolution laws of valley deformation during construction in the dam area. The law of valley deformation of the plunge pool behind the dam shows that the variation law of valley deformation at different elevations is similar. The shrinkage deformation has a good positive correlation with the elevation, and the deformation of the part with high elevation is relatively large. Both banks deform towards the river valley, showing a positive correlation with elevation. The deformation speed of the left bank is slightly faster than that of the right bank. The numerical simulation results of deformation are close to the field measured results. The research results can provide a reference for normal water storage in the later stage of the dam.