During the UHVDC transmission process, as the voltage level continues to rise, many problems caused by corona current cannot be ignored. From the perspective of statistical analysis and waveform shape, this paper sets the time domain indicator for the overall corona current on the transmission line for the first time, and proposes a set of indicator evaluation system to analyze the significance, rationality, independence and effectiveness of time domain indicators. The corona currents in different environments were successfully classified by using support vector machine. After the reduction analysis, three corona current indicators were selected, which in turn represent important information of the low, medium and high frequency bands of corona current. The corona current time domain indicator and the proposed evaluation method in this paper provide a new idea for the study of the overall corona current characteristics on the transmission line, which lays a foundation for the subsequent time-frequency joint analysis.