A commercial-scale Ocean Thermal Energy Conversion (OTEC) floating plant will be attached a large diameter Cold Water Pipe (CWP). There are concerns about unstable vibration and changes in the dynamic characteristic due to too large mass flow rate. Since the vibration may interfere development of larger capacity plant, comprehending the phenomena have generated considerable interest. The main objective of this study is to confirm whether the theory that describes the vibration of submerged fluid-conveying pipe reproduces the real phenomena through a tank experiment. We construct the experiment eliminated possible disturbances, and the free damping vibration of polycarbonate pipe of 4 m length is measured during water intake. In order to compare the experimental pipe and theoretical models, the damping characteristics are identified from the results without internal flow. As a result of the comparison, although the theoretical model using the inlet end condition reproduces basically reproduced the experiment, we observe a three dimensional nonlinear behavior that could not be predicted by the theory. We believe that this experiment will serve to improve the theories.