Considering the very vital function of railways, which is closely related to the safety of both humans and goods, railway vehicles are required to possess adequate structural capability so that they do not experience damage caused by operational loads. This study aims to analyze the structural strength of the underframe of a flat wagon designed to carry two of 20 feet containers using the finite element method. The analysis is conducted to determine the magnitude and distribution of stress, deformation, and the safety factor of the underframe structure under static loading conditions. The geometric modeling of the underframe is created using Autodesk Inventor 2020, while the simulation process is carried out using ANSYS R1 2022. The material used is S355J2 steel with a yield strength of 355 MPa. The applied loads include vertical, lateral, longitudinal, and combined loads in accordance with the EN 12663-2 standard. The simulation results indicate that the maximum stress remains below the material’s yield strength, the total deformation meets the maximum allowable limit of 0.5 mm within a 100 mm span, and the resulting safety factor ranges between 1.5 and 2.0. Based on these results, it can be concluded that the structural design of the 2×20-foot flat wagon underframe is considered structurally safe under static loading conditions.