Abstract: In this study, a numerical method has been developed to estimate the fatigue life of the vehicle chassis-components. The application of this method will significantly reduce the expenses for the required practical or in-service tests. In this method, firstly, using MATLAB, the real but random profiles for the standard roads have been produced on the basis of the random vibration theories, which give the spatial profile data in terms of time. These profiles have been used to study the dynamic behavior and to design the vehicle chassis. Then, a complete off-road-vehicle model has been developed and first-stage results have been used as input data to simulate the dynamic behavior of the model and to calculate the forces and displacements of the chassis structure using MSC.ADAMS. In this way, the optimum stiffness of the suspension system has been obtained. Finally, using the FEM based software; ANSYS, the stress distribution in a selected part-weldment (support of the front suspension system) has been obtained and fatigue life of the structure-components welds; joining the suspension system to the off-road vehicle chassis, has been calculated and the effects of the dynamic loads due to the road profiles have been studied.