Increasing demand for clean and effective energy production turns interests of the world on floating offshore wind technology. To establish floating wind farms, a wind turbine have to be mound on a floating structure. The floating structure has to be carefully design according to sea environmental condition and kept in precise position. Different types of floating structure and stationkeeping systems have been proposed for floating wind turbines. This project deals with design a spar floater with tension leg mooring system, where the vertical fairlead position located between center of buoyancy and center of gravity. In this project a details study about floater design and tension leg concept was presented. Further, a model was established in computer program RIFLEX and static and dynamic analysis was carried out for two different environmental conditions, one for an operation condition to understand the model behaviour in normal sea state. The second one was for extreme condition to estimate the extreme tether forces and find out slacking possibility.