The invention discloses a safety early warning system and method for maintenance of a 1000kV extra-high voltage AC transformer station, comprising a CPU, a power supply module, a wireless communication module, an alarm module and a display module. The safety early warning method is as follows: based on a three-dimensional map of a transformer station, a virtual electronic fence is planned with live equipment as the center, and positioning chips are arranged on maintenance workers, live equipment and maintenance tools; and the relative positions between the maintenance workers and the virtual electronic fence during the maintenance operation and conditions of actual operation steps are shown in the safety early warning system, when the maintenance workers mistakenly enter the virtual electronic fence and the actual operation steps do not meet the standard operation procedures, the alarm is started at the operation site and the safety early warning system at the same time, and the standard operation procedures are power cutting, electricity testing, ground connection, indication board hanging and fencing in the work area in order. The method realizes the standardized management of the transformer station maintenance work flow.