We can examine the validity of the wave-making resistance theory by the method of wave analysis. In order to investigate the discrepancy between the theoretical and experimental free wave spectrum, wave analysis was carried out for three Inuids, M-6, M-7 and M-8, at the speeds K ₀ L =14, 12, 10, 8 and its results were compared with theory. These Inuids were calculated from source distributions which were of the same form but different source strength. Therefore assuming linear theory they must generate free waves with the same form and linear relation between each other. As for the free wave spectrum of M-6 ( B/L =0.08), M-7 ( B/L =0.13), linear relation generally held but agreement was very poor between the phase and the amplitude at small θ of linear theory and experiment. Then the equivalent source distributions which gave the same free wave spectrum with the one obtained from wave analysis were calculated and compared with the theory.