Load flow (LF) is one of the most important parts to study and analyze power system operation. In this research paper, a detailed study for load flow analysis in distributed power system (DPS) is presented. A case study of modeling and simulation of the actual power distribution network is implemented with the electrical transient analyzer program (ETAP) software (version: 12.6). Furthermore, a comparison of common load flow techniques of power distribution is presented. In this assessment, numerical and practical methods including Newton-Raphson (NR), Fast Decoupled (FD), and Accelerated Gauss-Seidel (AGS) are provided and compared. The results (total generation, loading, demand, system losses, and critical report of load flow) are obtained and analyzed. This paper focuses on the detailed assessment and monitoring by using the most modern ETAP software, from high voltage substation (HVS) to the loads. The capability and effectiveness of load flow assessment are demonstrated according to the simulation results obtained with ETAP by applying it to the actual distributed power system of Tehran metro (subway). Once the modeling is performed in ETAP for complete power system, it might be highly beneficial for converting conventional grid into smart grid.