Abstarct: Nowadays, the electricity consumption tends to increase since the electrical energy can not be saved and also due to variable electricity demand during different hours of day, construction and establishing of pumped storage power plants has great importance. The project of Siyah Bishe pumped storage power plant with 1040 MW electricity production capability located in Mazendaran province, at 125 km from Tehran, is constructed on Chaloos river. The caverns are important parts of power plants. They are constructed and excavated in several steps due to large scale dimensions. The sequence of excavation in such constructions is one of the designers concerns. The numerical analysis is one of the recent approaches to determine the priority of excavation sequence. The selection of proper excavation sequence in the cavern of Siyah Bishe power plant using 3DEC software is the purpose of this research. First, the interaction of the caverns of the power plant and transformer is studied using the software. As a result, the excavation of these caverns donot affect on the other one. Therefore, only the excavation sequence of the power plant cavern associatd with the connected galleries was taken into account. For reducing of the running-time of the software, the cavern was divided into four sections; the excavation sequence is then analyzed separately for each part. For selecting the proper excavation sequence in the power plant cavern, 19 different models were built. The selection was preformed baxsed on the relative displacement of the power plant wall. The first part was selected and excavated, then selection of next section is started. Eventually, the obtained results of the software analysis were conformed to the results of instrumentation to validate the accuracy and reliability of the constructed models. As a result, there were negligible and insignificant differences