Abstract: To control tensions of pipeline without tensioner during installation of subsea flexible pipe, a hydraulic rotary driving system for deep-water flexible pipe reel has been developed on bases of the conventional closed hydrostatic transmission system. Firstly, mechanical structure of the driving system for deep-water flexible pipe reel is designed and the forces and movements of the system during oil pipeline installation are analyzed. On this basis, basic loop of the hydraulic rotary driving system is designed. By using MATLAB, the model for driving system for flexible pipe reel is established, including mechanical transmission elements, hydraulic driving system and tension-compensation control system. With consideration to various conditions and external loads expected during oil pipeline installation, simulation analysis is performed for the driving system to identify its performance in controlling and regulating tension of the oil pipeline during installation. Research results show that the proposed driving system can be deployed to cope with fluctuating external loads during offshore operations. In addition to ensure oil pipeline installation under constant tension, the system may be well coordinated with tensioners during operations in ultra-deep water areas.