The invention discloses a hydraulic multi-axis screwing device for flange bolts. The hydraulic multi-axis screwing device comprises a main frame body and an assistant frame body, and is characterized in that connection seats are arranged on both the main and assistant frame bodies, and can be directly connected with a mechanical arm of an excavator; the main and assistant frame bodies are connected with each other through a plurality of connection oil cylinders and positioning wheels; a plurality of groups of reduction gears and a plurality of hexangular sleeves are arranged in the main frame body; a plurality of hydraulic motors are correspondingly mounted on the outer side of the main frame body; the hexangular sleeves arranged in the main frame body are used for placing of the bolts; a plurality of hexangular sleeves, which are used for placing of the bolts, provided with no without teeth and capable of rotating, are correspondingly arranged in the assistant frame body; through driving of the hydraulic motors, the reduction gear groups and the hexangular sleeves arranged in the main frame body, the bolts can be effectively screwed. The hydraulic multi-axis screwing device is suitable for the work condition of the connection through a bolt which has high screwing torque, simple to manufacture, low in production cost, high in work efficiency and low in labor intensity, and has the advantage that the operating efficiency of a dredger can be improved.