Abstract: In order to make the calculation of lightning electromagnetic field closer to the actual status and simulate the lightning electromagnetic field in far zone, the analytical expressions of lightning electromagnetic field generated by oblique channel were derived with the dipole method, and the approximate relationships of lightning electromagnetic field and its derivative to channel-base current were obtained after approximate treatment of the exact analytical expressions for lightning electromagnetic field in far area. The waveforms of lightning electromagnetic field and its derivative from the exact and approximate results were compared based on the specified channel-base current described by a pulse function. The result shows that the difference between the exact and approximate waveforms decreases with the increase of the distance, and the applicable range for the approximate expressions of lightning electromagnetic field is stricter than that of the electromagnetic field derivative. The above result verifies the credibility of the approximate expressions, and provides the theoretical basis for the simulation of lightning electromagnetic fields in far zone.