To overcome the disadvantages of conventional dam deformation monitoring methods, which are high labor intensity, long cycle, and acquiring of only pointwise information, a recently developed technology, called ground-based synthetic aperture radar interferometry(GBInSAR), was applied to dam deformation monitoring. Based on an analysis of the GBInSAR system and imaging characteristics, a numerical model for atmospheric phase correction using a stable reference point was established and applied to monitor the deformation of the Geheyan Dam. The results show that at a location of 1 300 m downstream of the dam, atmospheric disturbance caused an error of up to 85 mm. Atmospheric disturbance interfering with the sight of radars was the main factor decreasing the accuracy of dam deformation monitoring with GBInSAR technology. After elimination of the influence of atmospheric disturbance, the results of dam deformation monitoring with GBInSAR technology agreed with plummet observations. The results also show that the deformation of the water release gate at the surface outlet was significantly greater than the dam body deformation, and it increased with the rise of the water level.