Since the use of seawater for the cooling system in the domestic nuclear power plant influences on ecological system of the coast, developed countries use the cooling system by natural draught cooling towers. Due to the enormous scale and sensible characteristics of the structure against thermal and wind load, the maintenance and the repair of the structural damage, besides structural safety, cause enormous costs. Therefore the durability design of the cooling tower becomes a new issue. In this study a 30 years old natural draught cooling tower with serious damage state was non-linearly analysed and the damage process was evaluated.