A PCI acquisition card based lightning current on-line monitoring device for overhead transmission lines is composed of Rogowski coils, a trigger circuit, a high-speed PCI acquisition card, an industrial control computer, GPRS modules, an energy taking coil, a charging controller, a storage battery and a voltage converter. The monitoring device is installed at a cross arm of a tower, and non-contact on-line monitoring is carried out for three-phase insulator strings of the transmission line tower and lightning conductors and lightning rods at the top of the tower; when lightning stroke happens near monitoring points, induced voltages are output by the Rogowski coils, various paths of lightning current signals are acquired by the device, data are sent to a terminal computer through the wireless communication GPRS modules for state evaluation, and lightning stroke fault locations can be accurately positioned; and due to the fact that the high-speed PCI acquisition card is used, sensitivity is high, and lightning signals can be accurately captured.