The aim of this paper is the computation of electromagnetic fields radiated by lightning witch is necessary in order to protect effectively the electrical and electronic systems against disturbances caused by this kind of discharges. In this paper we propose a hybrid method to evaluate the electromagnetic field associated to lightning return stroke current. This method is the combination of the images method and finite difference time-domain (FDTD) method. We calculate first, the magnetic field with images method (using the Simpson integration numerical method), and, secondly, the electric field based partially on the FDTD method. The lightning return stroke current is modeled by the engineering models. In this study we compare five lightning return stroke current models, namely the Transmission Line (TL) model, the Modified Transmission Line with exponential decay (MTLE) model, the Modified Transmission Line with linear decay (MTLL) model, Traveling current Source (TCS) model, and Bruce and Gold model (BG) model by assuming a common current wave shape at the channel base. In this work we have presented the influence of the variable speed of the return stroke current and the variable factor λ of the MTLE model on the computation of lightning electromagnetic field.