In this paper, a study about lightning electromagnetic radiation in a complex geometry is presented. Indeed, it is about examining the effect of a vertically stratified ground presence on the electromagnetic field generated by lightning strikes to a tall object (tower), using the three dimension Finite Difference Time-Domain (3D-FDTD) method. The space-time distribution of the current along the lightning channel and along the tower is modeled and calculated using the Transmission Line (TL) model extended in order to include a tall strike object. The developed computing code is validated by the comparison with the results obtained in the specialized literature. In this comparison, a satisfactory agreement between results is observed. According to the obtained results it is shown that both up-ground and under-ground electromagnetic field components (vertical and horizontal electric field and azimuthal magnetic field) magnitudes are affected by the presence of the vertically stratified ground.