Recently in various harbors, large and long period moored ship motions are caused by long period waves whose period are near to the natural period of surge. Rope breaking accidents, excessive compression and shearing deformations of fenders also happen in the case. So at an earlier stage, the moored ship is compelled to shift to offshore. In this paper, we propose a time domain analysis of moored ship motions in a harbor considering harbor oscillations and investigate the accuracy of the simulation by a field test for moored 90, 000DWT bulk carrier. It is clarified that the proposed time domain analysis of the moored ship motions considering harbor oscillations has a validity in accordance with the field test and some investigations.