For the lightning current waveform detection, both hardware trigger and software trigger have low reliability and the incompleteness of the waveform acquisition. According to the amplitude, slope and half peak time of lightning current, this paper proposes the lightning current identification method and cyclic trigger to improve the reliability of trigger and the integrity of the waveform detection. In this paper, the design and implementation of the lightning current online detection system was introduced in detail. It was used to detect the waveform, amplitude, polarity, lightning tower and lightning time etc. Finally, terminal PC was?programmed?in?C ?language, and the practicability of detection system was verified by experiments.