When the lightning electromagnetic wave propagates along the ground surface, the far field will be distorted due to the propagation effect, which will affect the accuracy of the lightning locating system. In this paper, the Wait’s analytical method was used to investigate the propagation effect of the finite ground conductivity and the Earth’s curvature on the lightning-radiated electromagnetic field. The far-field attenuation factors for different return stroke current waveforms and different conductivities were fitted, and the field-to-current conversion factor has been revised. The delay in arrival time of the far-field waveform caused by the propagation effect has been statistically analyzed. The results show that the effect of earth curvature cannot be ignored when the observation distance is larger than 200 km. Comparing with the case of flat ground, Earth’s curvature causes an additional attenuation of 9.6%, 29.4% and 55.5% of the field peak at observation distances of 200 km, 500 km and 1000 km, respectively. The ratio of the attenuated field peak to the ideal field peak decreases exponentially with the increase of the propagation distance, and the average value of the exponential decay constant is 1000 km. The steeper of the current wavefront, the more high frequency it contains, and the greater of the attenuation. When lightning-radiated electromagnetic field propagates along the land surface, with an increase of the propagation distance by 100 km, the delay in arrival time of the far-field waveform and the field peak is increased by 0.36 μs and 0.96 μs on average, respectively. It is concluded that, the propagation effect of the earth curvature needs to be considered for the long-range lightning locating and the measure of the lightning current parameters.