In order to extract the wave power, the floating cylinder has to satisfy the condition of being wave-free on one side when it is forced to oscillate in a given mode. In this paper the authors show the method of determing the contours which satisfy the above condition. Numerical calculations were carried out for the case of heaving and rolling mode, and these results show that the obtained contours have good performances for wave power absorption. The calculated results were confermed by the experiments for heaving mode.