The harm of pantographcatenary arc seriously hinders the development of highspeed railway. The pantographcatenary arc occurs frequently under the poor environmental condition. The pantographcatenary arc aggravates the wear of the slide plate and catenary wire, and the quality of current reception is decreased. In order to improve the safety and stability of highspeed railway operation, the dynamic characteristics of pantographcatenary arc under rainfall conditions were studied. Based on the selfdeveloped pantograph arcing experimental system, the current and voltage waveforms were collected under normal, light rain (rainfall 30 g) and heavy rain (rainfall 150 g) conditions, respectively. The pantographcatenary arc image was captured by using high speed camera. When working condition is constant, the arc is stretched and both arc area and circumference increase under rainfall conditions. The arc circumference and area are the largest under light rain conditions. The rainfall makes the current ripple increase. It also makes arc zerocurrent time become longer, and arc peak voltage increases. Therefore, the rainfall shortens burning time of the arc and increases the arc incidence rate, especially in the light rain environment. The arc power in rainfall environment increases. The minimum arc resistance appears near the peak value of the arc current waveform.The minimum arc resistance value in rainfall environment increases compared with that in normal environment.