Abstract: Affected by the weather, sea conditions and the structure of jack-up rig towed, the towing ability of tug is highly demanded in the towing operation. In the course of tug H towing jack-up rig K from well location 1 to location 2, the towing speed did not reach the expected speed, accompanied with the severe green water on deck and the stability of the rig being not good. Based on the calculation of the towing resistance of rig K under different sea conditions, together with the analysis of towing ability, the authors suggested the maximum speed of tug H when towing the rig K from well location 2 to location 3. This calculated result was consistent with the actual. By simulating the variable load, the authors also estimated the maximum uprising height of the leg when towing rig K on the premise of meeting the requirements of operation manual for the rig stability, which provides a theoretical foundation for the safe and high efficient towing operation.