In addition to the need for vertical and horizontal displacement observations，buildings need to be observed for deflection，which is particularly important for concrete dams，especially the double curved arch dams.The deflection observation refers to the horizontal displacement of each elevation point in the vertical section of a building relative to the base point of the base，and the vertical line is a simple and effective means to observe the deflection.Vertical monitoring，as an important means of dam deformation monitoring，has always been a key project for dam deformation safety data analysis and evaluation.Vertical line monitoring mainly uses horizontal and vertical plumb line to monitor horizontal displacement of dam.Based on the measured data of the vertical line of Shankouyan RCC double curved arch dam in the last 4 years，the variation of the horizontal displacement of the dam and the stability of the dam body are discussed and evaluated.The change of the horizontal displacement of the dam is directly affected by the changes of the environmental quantity and the water level of the reservoir.Based on the analysis of measured data，it is considered that the Shankouyan dam is stable.