In order to research the transfer characteristics of VFTO in GIS voltage transformer, this paper developed a Class B wave monitoring device which combined the generation of Class B to the shock wave、control and measurement into one, base on the limits on GIS transformer’s over-voltage and testing requirements in 《GB20840.1-2010 transformer General technical requirements》.Using this device to test the transmitted overvoltage of 110kV GIS Voltage transformer, the result showed that the device not only can meet the requirements of IEC and national standards, but also come to a conclusion that over-voltage transmission of GIS voltage transformer have a transfer characteristic.