The utility model relates to a GIS is with frequency homophase ac voltage withstand test testing system, its structure does, and excitation change, reactor, current -limiting resistor and capacitive voltage divider connect gradually and constitute the series resonance return circuit, and the series resonance return circuit links to each other with frequency transforming cabinet, the input of the output connection control case of series resonance return circuit and sampler, the output connection frequency transforming cabinet of control box, the voltage transformer low tension side on the operation generating line is connected to the input of sampler. The utility model discloses put up the ac voltage withstand test testing system of GIS equipment under adjacent not power failure of the generating line circumstances, made and carry out the experimental enable of GIS equipment ac voltage withstand test under adjacent not power failure of the generating line circumstances, carried out the very big convenience that provides for the withstand voltage test of system after enlargement, maintenance. Be suitable for and be widely used and promote at electric power system.