Seymareh dam was including double-arch concrete dams in the country. It has been constructed on the seymareh river In other to provide hydroelectric power, controling and regulating river flows and providing downstream water’s right. because of low river flow, dewatering takes a lot of time. This creates a temperature difference between part of the body into water and directly recive the heat water with the part of the body out of the water and heat recived from the sun passes. Because of this temperature difference, the heat distribution in the body are not identical and creats thermal starines and therefore creat thermal stresses. So if value of thermal stresses is exceeded from safety thermal stresses defined for dam, was causing spalling phenomenon and cracks in the body. While dewatering perform immediately, this difference temperature is negligible. In this study, using coding, has simulated seymareh dam and its surrounding in FLAC 3D software two method and the results have been compared with each other. In order to accommodation numerical model with the actual conditions, included all stages of the construction of the dam consist of primary balance backpacks influenced by gravitational sresses, reload gravity of the body and dewatering in numerical model. In the numerical simulation, is applied elastic behavioral model for dam body and mohr-coulomb behavioral model for backpacks and dam foundation. In the next step, to the hydro-mechanical and thermo-hydro-mechanical analysis, hydraulic stresses due reservoir water is applied to a distributed load on the dam wall and after applied thermal and mechanical boundary conditions, the model is solved. The results of hydro-mechanical and thermos-hydro-mechanical analysis displayed in terms of the stress and displacement diagrams of body and the results of numerical analysis has compared with data obtained by extensometers. Based on the results obtained, in the case of body to be built and solved in layers compared with the case when the whole body at once resolved, occurs 30% reduction in Stress. By entering the hydraulic power at the different levels are added approximately 18% of the tensile stress to the reservoir without water. As a result, the minimum tensile stress occurs when the reservoir water level is less than 80 meters and more than 10 meters. By applying heat distribution, added 25% of the tensile stress compared to hydro-mechanical. Generally the tensile stress more than the allowable tensile stress is considered and high probability of tensile cracks in the central part of the body. The overall displacement of dam is good agreement with the results of the instruments.