In the present study, the weight-based cost optimization of tension leg platform (TLP) is performed under design constraints. The effect of tsunami on the TLP is observed to be greater significance and is investigated here. The design constraint includes tether tension limitation at the bottom end. The optimal material cost of TLP is obtained through a gradient-based optimizer-sequential quadratic programming. The tether tension is evaluated using Nordgren’s model. It is observed that the optimal area of tether and the diameter of column is extremely sensitive to significant wave height. The results show that by properly regulating the minimum tether tension a gross saving in material cost can be achieved. Furthermore, a representative curve is developed, from which one can obtain the approximate cost at a given significant wave height and chosen tether tension value. This may help designers in setting budget for a given location governed by the significant wave height.