In this paper, a method based on electromagnetic simulation is presented to investigate the vehicle penetration loss in a train for a given illumination source on the broadside at 819.125 MHz. Since the vehicle has a size of 31.4λ and is referred to as electrically large, parallel Method of Moments (MoM) with higher order basis functions (HOB) is used in order to obtain an accurate result in an efficient manner. Using simulation, the power level inside the train can be computed and the path loss can be evaluated. Compare to measurement this method provides more detailed information in the entire region of concern and is helpful in the configuration of the relevant communication system between in-vehicle devices and outside base station.