Abstract: The near-field electric field of lightning has the characteristics of transient and high intensity. In the standard specification of lightning protection, the electric field at different distances from the lightning channel should be clearly specified. Based on the transmission-line (TL) model, the variation of the electric field peaks and its variation rate with the distance in the near field of lightning is studied, and the approximate expressions are simplified, and compared with the measured data reported in the related literature. The results show that the results calculated by the approximate expressions are consistent with the data reported in other literatures, as well as the data measured by SLOT observation team. The approximate expressions can characterize the electric field and its variation rate within 1 km, and thus provide technical support for lightning protection engineering.