With the requirement of meticulous management of power line loss put forward by our country, it is necessary to increase the level of line loss management by adding intelligent metering devices. In recent years, the common layout of low-voltage distribution network metering devices (mainly low-voltage smart meters) has been quite perfect, and the rules and means of its verification and field calibration have been quite perfect. But, As the power grid company"s requirements for the power failure assessment indicators are getting higher and higher, the rate of increase or replacement of high-voltage (6-35 kV) metering devices is far less than that of low-voltage meters. Because of unable power cutting, field calibration of high-voltage metering devices that have been in operation for many years only at the meter section, not including the PT, CT. So, there is no means to obtain the integrated error of the high-voltage metering device. In this paper, a new type of on-site calibration device for live operation is studied by studying the operation status of existing metering devices in high-voltage distribution network. It can not only field calibrate the existing high-voltage metering devices, but also achieve the accuracy of 0.1 level of active power in the dynamic range of 5-500 A.