The invention discloses a PBI-KOH anionic conductive polymer electrolyte-based all-solid supercapacitor and a preparation method thereof. The PBI-KOH anionic conductive polymer electrolyte-based all-solid supercapacitor is characterized by being prepared by adding a current collector and then assembling a KOH-doped PBI (polybenzimidazole) anionic conductive polymer as an electrolyte, a KOH-doped PBI anionic conductive polymer membrane as the membrane, an Ni(OH)<2> nanosphere as a positive material and activated carbon, mesoporous carbon or a carbon nanotube as a negative material. The supercapacitor disclosed by the invention achieves a real alkaline all-solid-state; a liquid electrolyte does not need to add to the used polymer electrolyte; the using safety and the practicability of the supercapacitor are improved; and compared with a traditional gel electrode quasi solid supercapacitor, the PBI-KOH anionic conductive polymer electrolyte-based all-solid supercapacitor has better super capacitive property.