The present invention discloses a high-concentration organic wastewater treatment reactor. A lower water distribution system, an upper water distribution system, a lower three-phase separator and an upper inclined plate separator are provided from bottom to top in a reactor body of the high-concentration organic wastewater treatment reactor. A gas-liquid separator is disposed on the top of the reactor body. The lower water distribution system and the upper water distribution system are connected to an influent pipe. A lower biogas ascending pipe connected to the gas-liquid separator is disposed on the top of the lower three-phase separator. An upper biogas ascending pipe and an effluent pipe are disposed above the upper inclined plate separator. An outlet end of the upper biogas ascending pipe is connected to the gas-liquid separator. A downcomer is disposed on the bottom of the gas-liquid separator. An air pipe is disposed on the top of the gas-liquid separator. The reactor of the present invention has the characteristics of low energy consumption, good effluent water quality, large biogas production, and no odor, is capable of enhancing the even water distribution and fully mixing sludge and water, have a high removal efficiency of pollutants. Moreover, an internal circulating water dilutes influent water. A system having a strong impact resistance ability and a reactor being operated stably for a long term are achieved.