Abstract: Due to different shipyard conditions and location environment conditions of different shipyards, the unlocking method for semi-submersible crane and pipe-laying vessel varies. The impact of load caused by wind, wave, and flow must be taken into account during the unlocking process. In order to ensure safe unlocking, it is important to solve the problem of calculating the towing resistance. We analyze three different calculation methods for towing resistance, i.e.，the one based on empirical formulas, the one based on the dynamic model of wind and flow, and the one based on Guidelines for Towage at Sea. The calculation results obtained by these methods are compared. Suggestions are given on the basis of analysis results.