The present invention relates to an electronic transformer error testing device. The electronic transformer error testing device comprises an acquisition unit, a synchronization unit, an arithmetic unit, a transmission unit and a server; the acquisition unit comprises an electronic transformer and the like; the synchronization unit outputs synchronization signals to the primary signals of the electronic transformer, the secondary signals of an operating electromagnetic transformer and the arithmetic unit; the arithmetic unit is used for calculating the effective values, phases and frequencies of the primary signals of the electronic transformer and the secondary signals of the electromagnetic transformer and performing real-time angle difference and ratio difference calculation so as to obtain real-time comparison error data; the transmission unit is used for exchanging the obtained real-time error comparison data with the background server; and the server is used for displaying the real-time comparison error data. The device can perform real-time data monitoring, historical data query and data analysis on the error of the electronic transformer and can be used for solving the problem of electronic transformer on-line error measurement.