The invention discloses a multi-functional bolt locking processing and bolted hole repairing device for a pressure vessel of a nuclear power plant. The device comprises a lathe body, a horizontal numerical-control boring-milling machining component, a vertical numerical-control boring-milling machining component and a conversion device. The horizontal numerical-control boring-milling machining component comprises a spindle motor. The vertical numerical-control boring-milling machining component comprises another spindle motor. The conversion device is used for realizing the mutual conversion of the horizontal numerical-control boring-milling machining component and the vertical numerical-control boring-milling machining component. The conversion device is connected onto the lathe body, and comprises a torque motor and a spacing device. The torque motor is used for providing conversion torque to enable the spindle motors to rotate. The spacing device is used for spacing the rotation positions of the spindle motors. The torque motor is connected with the spindle motors. Through the implementation of the device, a bolt locked in the pressure vessel can be quickly and safely taken out, the repairing operation of a bolted hole is completed, the in-situ repairing efficiency can be improved, the structure is compact, the operating precision is high, the operating speed is high, and the safety and the reliability are high.