Evaluation of Settlement for earth and rockfill dams during the construction, the end of the construction phase as well as the first impounding period as one of the most critical times during the life of the dam are always significant for geologists, geotechnical engineers and dam designers. Based on this purpose, in this research paper, the behavior of Rudbar lorestan earth rockfill dam using the results of monitoring and back analysis using FLAC 2D software (FDM) has been considered. In order to evaluate the accuracy of amount of dam's geotechnical design parameters considered in the dam construction process, the numerical modelling and prediction the amount of dam's geotechnical design parameters of actual soil condition of the dam construction, which is named back analyses or back calculation was carried out. The results from monitoring are input parameters for the numerical modeling. Mohr-Coulomb Elastoplastic behavior was the suitable numerical modeling of Rudbar dam which is according to the results of the analysis and the data obtained from instrumentation readings. In this research, there was a good agreement between the results of numerical model and monitoring results in addition, the obtained values from back analyses of numerical models was with confidence.