The invention discloses an oil level online monitoring system for a high pressure oil insulation device. The oil level online monitoring system includes: a monitoring acquisition unit which may be a flexible bent circuit board, is positioned in an oil level meter of an insulation oil device, and is used for monitoring and acquiring oil level state data of insulation oil in real time and sending the oil level state data to a wireless receiving and analyzing unit; the wireless receiving and analyzing unit which is used for receiving the oil level state data, comparing the oil level state data and a preset threshold to acquire the comparison result, and sending the oil level state data and the comparison result to a background monitoring unit; the background monitoring unit which is used formanaging the oil level state data, and determining if alarm information is sent out or not according to the comparison result. The oil level online monitoring method is convenient, reliable, and stable, can ensure the accuracy of oil level state monitoring, can send an alarm according to the comparison result while abnormal phenomena occur, can reduce the site operation and maintenance cost, can provide convenience for on-site operation workers, and can ensure the safe and reliable operation of a power grid.