Dam stress and strain monitoring is a necessary and important monitoring project for Large arch dam. A large arch dam in Zhejiang, China was monitored for 20 years by using differential resistance strain gauge and non-stress gauge, and then the stress of the dam was calculated by deformation method. The results show that the dam is dominated by compressive strain and compressive stress, and is significantly affected by temperature. The maximum compressive strain of the dam is −377.52 με, and the maximum radial compressive stress is −4.46 MPa. The tangential maximum compressive stress is −4.42 MPa and the vertical maximum compressive stress is −3.30 MPa.