The　air　gap　of　the　insulation　system　is　the　main　source　caused　partial　discharge　(PD)　in　high　voltage　power　equipment　made　of　oil-paper　insulation　material.　In　general,　there　are　two　kinds　of　air　gaps,　which　come　out　from　solid　insulation-paper　board　because　of　manufacture　process　and　liquid　insulation-bubbles　in　oil.　To　investigate　the　characteristic　of　PD　in　oil-paper　insulation　under　direct　current　(DC)　voltage,　this　paper　presents　the　air　gap　model　of　paper　board　and　bubbles　model　in　oil　with　oil-paper　insulation　system　respectively.　The　partial　discharges　of　these　models　are　measured　by　Rogowski　coil　and　sampling　resistor　under　direct　current　voltage　in　the　laboratory.　The　partial　discharge　pulses　are　analyzed　and　processed　by　Origin　software　such　as　frequency　spectrum　and　filtering.　The　characteristic　of　PD　pulses　of　the　air　gap　in　oil-paper　under　DC　voltage　are　described　in　the　end.　These　results　lay　the　foundation　for　the　PD　measurement　and　recognition　in　oil-paper　insulation　system　(such　as　converter　transformer)　under　DC　voltage.