Abstract: The tendon system is used to moor TLP, and it is an important part of TLP. The analysis of the tension leg in installation and in-place conditions must be done to guarantee the safety of the platform. During the installation tendons mainly undergo current and wave loads, and in the in-place state, the tendons are also affected by the platform offset. In order to accurately calculate the internal forces of a tension leg it is necessary to build the model of tendon in installation and in-place states and apply the fully time-domain analysis method. According to the complex structure of tension leg, kinds of loads applied on tendon including wind, current, wave load, hydrostatic pressure and weight, etc. and internal forces of the tension leg are obtained by numerical analysis. The maximum internal force of the tension leg under different conditions is given. According to the calculation results, the global strength of tension leg is evaluated by the design standard.