The utility model discloses a forced grounding auxiliary device of a series resonance voltage withstanding system. The power plug is connected with a three-phase power supply. The output socket is connected with a voltage-withstanding instrument; a power plug, an output socket, a first relay execution end and a second relay execution end are connected in series. The input end of the power conditioning module is connected with a power plug; the output end of the power supply conditioning module is connected with a first relay control loop and a second relay control loop; a grounding groove of the first relay control loop is connected with an insertion piece and a grounding terminal, the grounding terminal is connected with a grounding terminal of a voltage withstanding instrument, a microswitch is arranged in the first relay control loop, the insertion piece controls the microswitch, the insertion piece is grounded through a detection loop, and the detection loop controls a second relaycontrol loop through optical signals. According to the utility model, reliable spectrum grounding guarantee is provided for a voltage withstanding instrument, hidden safety troubles caused by misoperation can be prevented through multi-channel detection, and the safety is improved.