Abstarct: Earth dams are one of the most important and complex engineering structures that cost a lot of money to study and implement these projects, so addressing their safety issues while constructing and also during the utilization period is of particular importance. Continuous behavior assessment of dam is necessary to prevent dam collapse due to various factors. For this purpose, by using instrumentation and installing them in appropriate places and periodic reading of data along with their reversal analysis, one can predict the most certain factor of inevitality and take the necessary measures in order to deal with it. On the other hand, using numerical methods, the dam model can be created in the software environment and the stability of the dam against different factors for different conditions of the dam, both in terms of hands and in terms of the characteristics of the materials used in the core and ... For the dams implemented and the dams being designed were investigated and achieved an optimal state. Providing real information about the actual behavior of the dam and comparing it with design predictions can be very useful in evaluating the accuracy of the theories and assumptions used. Also, by extracting the model that is most consistent with the actual model, it predicted the behavior of dams in the future. In this research, using quatrain analysis (using Geo Studio software), which is one of the most accurate and up-to-date methods for analyzing earth dams, the stability of earth dams in stable oozing state, the end of dam construction and semi-filled reservoir was investigated. For this purpose, the cross section of Damghan Dam was selected as a case study for analysis and modeled by SLOPE/W and SEEP/W software from Geo Studio software package. Then, the numerical model was confirmed by instrumentation data and analyzed. Static and quasi-static stability of upstream and stable milk and control and reliability coefficients obtained were compared with the U.S.S.CORPS of ENGS standards.