Abstract: The accurate operation of gateway electric energy metering device is directly related to the accuracy of electricity trade settlement. In addition to the accuracy of gateway watt hour meter, metering transformer and metering secondary circuit, the normal operation of voltage switching relay also affects the accuracy of metering. Taking a typical case of metering inaccuracy caused by voltage switching relay failure as an example, the event process, causes and results are analyzed in depth. The electricity quantity balance method and correction coefficient method are used to calculate the error electricity quantity. Combined with the event itself, the errors of the two calculation methods are analyzed. It provides an important reference for the calculation of wrong electricity quantity due to measurement inaccuracy caused by similar faults.