The normal calibration method of electronic voltage transformer (EVT) is Offline calibration, and it requires complex outage switching operations which will bring large economic losses. This paper studies on-site calibration system of 220kV electronic voltage transformer, including standard channel, calibration channel and calibration system based on PC. An adaptive full-phase DFT algorithm is proposed to calculate electric parameters, extract the frequency of the grid accurately, adjust the DFT operation points, and approximate the non-synchronous sampling to synchronous sampling. In this paper, a set of "standard capacitor fully insulated lifting access device operated by wireless remote control, and the security simulation analysis is carried out. Test shows that the system ratio error is less than 0.05% and phase error is less than 2′, and it ensures the security of capacitor standard’s access and exit, which meets the requirement of 0.2 class electronic transformer online calibration system.