The Capacitor Voltage Transformer (CVT), which has advantage of dielectric strength and insulation margin, is widely used at 110 kV and above voltage level power system at error measurement, system protection and so on. With the separately of power plants and transmission grid, people has been pay much more attention on accuracy of gateway energy metering device. Actually, the error data often vary greatly with different working conditions because of the structural characteristics of CVT. First, equivalent model has been established through by considering the structural principle of CVT, measuring instruments and external environment to take theoretical analysis for error. Second, take CVTs which are used at Zhe Fu project for example to contrast error data of delivery test, commissioning test and online error calibration. Then, these measured data have proved the correctness of the theoretical analysis. The analysis of CVT error data trend and validation tests provides guidance for commissioning test and online error calibration. What"s more? It improves the reliability of CVT error measurement.