The invention discloses a gas insulation-based combined high voltage generating device. The device comprises an alternating-current power source unit, a direct-current power source unit, an output voltage lead-out and measurement unit, and an output unit; the alternating-current power source unit is used for generating an alternating-current voltage; the alternating-current power source unit is packaged in an SF6 gas insulation unit; when the output of the direct-current power source unit is grounded, the alternating-current voltage is outputted to the output unit; the direct-current power source unit is used for generating a direct-current voltage; the direct-current power source unit is packaged in the SF6 gas insulation unit; when the output of the alternating-current power source unitis grounded, the direct-current voltage is outputted to the output unit; and the alternating-current voltage and the direct-current voltage are led out through the output unit. According to the gas insulation-based combined high voltage generating device, when the alternating-current power source unit and the direct-current power source unit are combined to output the voltages, the high-voltage end of the direct-current power source unit and the alternating-current power source unit are connected in series. The structure of the gas insulation-based combined high voltage generating device is simple. The alternating-current voltage and the direct-current voltage generated by the gas insulation-based combined high voltage generating device can be synchronously adjusted.