The invention discloses an in-transit grounding grid current detection device. The device is composed of a single-chip microcomputer IC1, a display output module IC2, a sampling current transformer CT1, a wire, a battery, a jointing clamp and a divider resistor, wherein a far-end grounding point 1n and a near-end grounding point 2n of an in-transit grounding grid are connected into the device through the wire and the jointing clamp respectively, the single-chip microcomputer IC1 responds to a measurement interruption service request generated by a key biswitch K1 and controls opening and closing of an electronic switch K2 through a port IO1 in a measurement interruption request service program of the single-chip microcomputer, an open-circuit voltage and a short-circuit current between 1nand 2n are measured through ports AD1 and AD2, equivalent resistance, an equivalent current and equivalent power between the grounding points 1n and 2n are calculated according to the Thevenin theoremand the Norton theorem, and the single-chip microcomputer performs communication with the display output module through a serial port, sends a measurement result and receives a user setting value.