It is important to study the wind forces-lift, overturning-moment and drag-acting on the deck of semi-submersible oil rig, because she usually is operated at rough sea. When we consider her role over the free surface, she is divied into three parts, deck, column and superstructure. For safe operation of her, it is expected to clarify the mutual interaction about the wind forces among them. The estimation method for the wind forces of the deck has not been established. Under the shelter of column and superstructure, the wind flow near the deck surface is very complicated. The experiments about the effect of column and superstructure on the wind forces acting on the deck have been carried out and the calculation to estimate them has been performed by using the simple flow model around the deck. In this paper, the results of them are presented.