A procedure for calculating added resistance on a virtical circular cylinder in regular waves is presented. The linearized velocity potential for around a model is given by source distribution on discrete panels representing the body. Momentum relations, Maruo's theory, are used to derive general results in terms of Kochin function with the effect of line integral. These computational results in momentum theory show that the effect of line integral on added resistance cannot be neglected. At the same time, another evaluation of the drag force on the model is performed by integrating the pressure directly on the surface of the body. These analytical results for the model in head and following sea conditions are compared with experimental results.