The invention discloses a high-speed motorized spindle loading and knife replacing test device, belongs to the technical field of mechanical testing, and aims at solving problems that the number of functions in the prior art is small, the price is high and a real installation environment cannot be simulated. The device comprises a horizontal iron, a supporting rack, a main shaft supporting part, a main shaft torque loading part, a single-hydraulic-cylinder bidirectional cutting force loading part, and a knife replacing system part. The supporting rack is fixed on the horizontal iron, and the main shaft supporting part and the main shaft torque loading part are vertically fixed on the supporting rack. The main shaft torque loading part is connected with a motorized spindle of the main shaft supporting part, thereby achieving the torque loading. The motorized spindle is arranged vertically, and the single-hydraulic-cylinder bidirectional cutting force loading part is fixed on the horizontal iron, and acts on a loading unit of the main shaft torque loading part, thereby achieving the bidirectional cutting force loading. The knife replacing system part is fixed on the supporting rack.