The invention provides a 750kV level capacitive voltage transformer onsite calibration system and calibration method, belongs to the technical field of transformer detection, and mainly solves the requirement of an onsite 750kV level capacitive voltage transformer for source tracing of higher precision and problems that a voltage boosting device is difficult in voltage boosting in onsite verification and liable to be interfered by electromagnetism. The 750kV level capacitive voltage transformer onsite calibration system comprises a standard device, a variable-frequency electron source, a transformer calibration instrument and an analog load device. The 750kV level capacitive voltage transformer onsite calibration system is characterized in that the standard device comprises a standard voltage transformer and an inductive voltage divider. The standard voltage transformer is composed of a standard voltage transformer primary winding, a standard voltage transformer voltage boosting winding and a standard voltage transformer secondary proportional winding. The inductive voltage divider is composed of an inductive voltage divider primary winding, an inductive voltage divider secondary power supply winding and an inductive voltage divider secondary proportional winding. The analog load device is composed of a first standard load, a second standard load, a metering winding, an instrument winding switching relay, a first standard load working relay and a second standard load working relay.