Abstract: To analyze the coupling effects of typical high power electromagnetic environment on overhead cables, the parallel finite difference time domain(FDTD) algorithm is used to calculate the induced current and voltage on the cable under the lightning electromagnetic pulse(LEMP) and two kinds of highaltitude nuclear electromagnetic pulse (HEMP) environments. The variation of the coupling effect of overhead cable with different cable lengths, different polarizations of the incident wave are analyzed. The results show that the strongest coupling occurrs when the direction of the incident wave is along with the cable and as the cable length increases, the rising edges of the induced current and terminal voltage are almost unchanged, but the waveforms are amplified and broaden. There is no future increase in the peak of induced voltage, when the line length increases to be equivalent to the corresponding wave is most concentrated.such a cable length can reach several miles for LEMP, hundreds of meters for HEMP1 (Baer wave), and tens of meters for the wide band HEMP2 (IEC 100029). It also shows that under the same conditions, the LEMP coupling effect is strongest, followed by HEMP1, HEMP2.