The invention provides a comprehensive detection system and method for an electric transmission line grounding system. The system is characterized in that eight pairs of voltage transformers and current transformers are arranged on four grounding down leads of a tower and overhead lightning wires on the left end and the right end of the tower in pairs in an adjacent manner; the annular voltage transformers arranged on the lightning wires apply a voltage to the lightning wires and the annular voltage transformers arranged on the four grounding down leads of the tower collect the voltage signalsthereof and send the signals to a grounding resistance test device; the annular current transformers collect eight groups of current signals of the four grounding down leads of the tower and overheadlightning wires on the left end and the right end of the tower and send the signals to the grounding resistance test device; the grounding resistance test device calculates a contact resistance value. According to the invention, four grounding down leads of a tower and overhead lightning wires of the tower are used as measuring points together for comprehensive detection of the resistance of a tower body and a grounding body.