The invention discloses a three-phase separator for a biomass pyrolysis liquid boiling-bed reactor and application of the three-phase separator. The three-phase separator is mainly formed by coaxial arrangement of a bearing shell of a reactor, a liquid-solid cyclone separator and an inverted-conical-shaped baffle; the liquid-solid cyclone separator is arranged at the upper portion of the bearing shell, the inner wall face of the bearing shell surroundsthe periphery of the liquid-solid cyclone separator, the inverted-conical-shaped baffle is arranged below the liquid-solid cyclone separator, and the liquid-solid cyclone separator is provided with an independent gas-phase outlet and an independent liquid-phase outlet. The three-phase separator is suitable for a three-phase mixture prepared from a separating gas phase, liquid phase and catalyst in the hydrodeoxygenation boiling-bed reactor with biomass pyrolysis liquid as raw oil, and has the advantages that the three-phase separation efficiency and speed are high, the operation elasticity is large, the three-phase separation space is small, and the utilization rate of the reactor is high.