The forced rolling model test has been studied for the oil tanker under three rolling amplitudes with rolling period from 0.8 s to 20s by using self-developed equipment and control system of the rolling test. The forced rolling moments and the phase shifts between the rolling moment and the rolling motion is comprehensively studied under the different rolling periods at zero sailing speed. The test results show that the rolling moment firstly decreases with the increase of the rolling period until it reaches to the minimum rolling moment when the test period approaches to the natural rolling period, and then increases gradually. Finally the rolling moment will remain constant when the rolling period becomes very long and the ship rolls slowly. The rolling moment is multiple relation with the rolling amplitude with the same rolling period and the different amplitudes. The added inertia increases linearly with the reduce of the rolling period, but the rolling damping increases nonlinearly with the increase of the rolling amplitude.