Lightning electromagnetic pulse is one of main causes of lightning disasters, so the electromagnetic environment assessment is important for protection. Although there is plenty of commercial electromagnetic simulation software on market, most of them have strict system requirements on the computing environment and are timeconsuming for users to build a reasonable model. Traditional commercial software is not suitable for daily lightning protection and evaluation services. For solving this problem， an efficient approach for electromagnetic environment assessment under direct lightning strikes is proposed based on the FiniteDifference TimeDomain (FDTD) method. Simple examples are also provided. It is of great significance to the further research in the field.