Disclosed is a simulated electric field test method for a transmission line on-line monitoring device; the transmission line on-line monitoring device (1) is positioned in a high voltage electric field laboratory (2) and runs, and the device (1) is in wireless connection with a monitoring host background system outside the laboratory (2); the monitoring device (1) is imposed with a simulated electric field; and the wireless transmission data consecutively transmitted before and after the imposition of the simulated electric field is detected. The invention provides the detection indicators which are tallied with the actual operating conditions and extremely provided with operability to ensure the reliability and stability of the monitoring device (1) under high-voltage electric field circumstances. The simulated electric field test method is simple to operate, while the detection indicators are tallied with the actual using conditions of transmission line monitoring and can be used to check the actual use performances of various on-line monitoring devices in high voltage transmission lines, so that the simulated electric field test method has a wide application range.