We analyzed the possible lightning electromagnetic pulse (LEMP) caused by a lightning strike on a petrochemical plant, based on the modified transmission line model with linear current decay with height. The LEMP caused by a lightning strike with a 100 kA lightning current was calculated using the finite-difference time-domain (FDTD) method. The results indicate that the overground waveform of the horizontal electric field varies greatly because of the influence of ground reflection, while the underground waveform changes slightly, primarily a change in magnitude. The difference of the vertical electric field amplitude between above the ground and below the ground is very large, and the overground waveform change slightly with height, and the first peak of the underground waveform reduces with an increment of depth, but the second peak increases with an increment of depth because of the influence of ground reflection. The horizontal magnetic field changes regularly, which below ground changes slightly with height and decreases with the increment of distance to the lightning channel, but the underground horizontal magnetic field decays smoothly with an increment of depth. At a height of 10m above ground, the peak of the horizontal electric reaches more than 110 kV/m at 10 m away from the lightning channel, the vertical electric field reaches 240 kV/m, the horizontal magnetic field reaches 230 0 A/m, and the powerful LEMP is a severe test to lightning protection design of petrochemical enterprises.