Lightning transients in wind turbine are the most important phenomena when conducting insulation coordination studies. However, models and methods recommended by international organizations are insufficient and still under investigation. Lightning overvoltage in wind turbines requires a broad knowledge on numerical methods of computing electric field, dielectric breakdown, electromagnetic transients and characteristics of lightning current. This paper deals with the simulation of lightning overvoltage of wind turbines by using EMTPIATP. Simulation results suggest a practical procedure of lightning protection for an existing wind farm in Vietnam. Electrical behavior along the mitigation path and in the connected grid will be estimated in order to investigate the effect of lightning current parameters and lightning location in the wind farm.