In order to estimate the seismic safety of existing arch dams, it is essential to assess the static behavior and the mechanical resistance of arch dam. Numerical analysis model for transverse joints (contraction joints) of the arch dam is developed considering the separation, sliding and re-contact behaviors of contraction joints. The static behaviors of an arch dam under annual change of temperature and water level were calculated by using non-linear three-dimensional finite element analysis method that incorporated the developed numerical analysis model of contraction joints. The displacement of the dam body was compared both in analysis and in measured data. At a result, the calculated results can give a good estimation for dam deformation of an existing arch dam caused by those loads. In addition, the effective arch zone was formed under consecutive contraction joints. Thus, the nature of load capacity mechanism was identified. Using these calculated results, the numerical prediction on the displacement of an existing arch dam was proposed for daily management.