Based on the two-dimensional finite-difference time-domain method (FDTD), this paper constructs a lightning electromagnetic wave propagation model under real terrain, studies the influence of the mountainous terrain in Hainan Province on the lightning electromagnetic wave propagation, and then proposes the asynchronous Long terrain envelope and time compensation method to correct the lightning positioning error. The simulation results show that: 1) Mountain terrain will significantly change the peak size and rising edge time of the tangential magnetic field. Compared with the change that happens under the flat surface conditions, the maximum change in tangential magnetic field waveform peaks decreases by 38%, the rising edge time increase ranges from 1- to 3 μs, peak arrival time lags behind that of the flat conditions, and after filtering wave treatment, magnetic field peak decreases, waveform becomes steep, rising edge time is reduced. 2) In terms of the peak-by-peak method, the positioning error of lightning strike points in the real terrain path is significantly larger than that of the flat ground, while in terms of the interrelated algorithm method, the positioning error under the real terrain path is larger than that in the flat-ground situation, but the difference between the two positioning errors is not significant, for the positioning error caused by the peak-by-peak method larger. 3) Overall, the use of 5km envelope gets better revision effect, positioning errors are within the 100 meters magnitude, for compared with other algorithms lightning positioning accuracy has been greatly improved.