A two-dimensional fractional Brown motion (fBm) model was used to describe the irregular terrain, and the Longmire-Scott soil-parameter frequency dependent model was applied to investigate the propagation effect of soil moisture on the lightning vertical electric field over irregular terrains. Main results are as follows:(1) The surface irregularity can lead to the attenuation of the magnitude of the vertical electric field and lags of the rise time of the field waveform. With the increase in the surface irregularity, the attenuation of the vertical electric field intensifies and the rise time of the field waveform increases. (2) Regardless of the degree of surface irregularity, increases in the soil moisture will reduce the attenuation of the vertical electric field. (3) Generally, increases in the surface irregularity and decreases in the soil moisture can result in stronger attenuation of the vertical electric field and longer rise time of the field waveform.