During an up-righting project for a capsized ship, the dynamic effect enlarges the tensions of cables. The cable tensions which are calculated based on statics and the safety evaluation which is based on these tensions cannot ensure the safety of the up-righting project. Due to the above reasons, a numerical simulation project is applied to investigate the dynamic effect on cable tensions of up-righting projects and evaluate the safety of up-righting project in current research. Firstly, a theoretical equation of the quasi-static up-righting project model is established in current research and is solved. Subsequently, the precision of the numerical simulation method applied in current research is checked by comparing cable tensions which are calculated by theoretical model and numerical simulation method. The cable tensions in different cases are solved by the numerical simulation method which accounts for dynamic effect in order to investigate the relationship between cable tensions and capsized ship weights, cable stiffness and winding-in speed. Finally, the safety of up-righting project is evaluated based on all the cable tensions calculated. It is pointed out that cable tension increases with the value of capsized ship weight, cable stiffness or winding-in speed approximately. The safety coefficients of cable in some high winding-in speeds are bellow 1.0. The results indicate that the dynamic effect is significant and should be accounted for during the up-righting project.