The invention puts forward a gear box characteristic parameter real-time on-line detection device comprising a platform base, a drag control module, and a system monitoring module. A power input motor, a loading motor, a tested gear box and an accompanying gear box are installed on the platform base, and the accompanying gear box and the loading motor provide an analog load for the tested gear box. The drag control module comprises a power input motor controller, a loading motor controller, a first inverter and a second inverter, and the first inverter and the second inverter are connected by a DC bus. The system monitoring module comprises a sensor data acquisition unit and a system monitoring software which is in control connection with the sensor data acquisition unit and the drag control module, wherein the sensor data acquisition unit acquires data information of the tested gear box and the accompanying gear box and sends the data information to the system monitoring software, and the system monitoring software displays, stores and analyzes the data information.