Abstract: In traditional study of concrete high arch dam deformation state, the influence of reservoir basin deformation far away from dam site is neglected, which causes the difference of the deformation calculation results and monitoring data. Through establishing FEM model for a wide range of reservoir basin, the method to analyze the influence of reservoir basin deformation on dam deformation was put forward in consideration of a reasonable model range. Taking a high concrete arch dam as a research object, a reservoir basin FEM model and a near-dam area FEM model were used jointly to simulate the influence of reservoir basin on dam body deformation. The research results show that when the reservoir bedrock lithology is poor, the influence of reservoir basin deformation of high dams on the dam body is significant, and the deformation value obtained by this new method that takes into consideration of the reservoir basin deformation is closer to the measured value.