This paper studied on inner tank flow of the LNG bunkering vessel to analyze the repercussion on the ship motion. Also, devices which are able to reduce roll motion of the ship were invented, and efficiency of them was verified by conducting model test in 2D wave tank and using CFD(Computational fluid dynamics) analysis. Star ccm+, which is commercial CFD analysis program, was used to solve the FSFI(Fluid - Structura - Fluid interaction) problem : incident wave - ship motion - inner tank flow. At that time, the two fluid areas were modeled differently in two and three dimensions respectively to decrease calculating time. In the experiment, moreover, roll motion of the ship was analyzed with numerous cases, which are varying according to inner tank filling ratio and shape, on regular and irregular waves. There are swash hole and bulkhead in the tank, and the performance of the optimized these devices which shows up to 61% reduction of roll motion was confirmed. Also, the experimental results for cylinder type tank in the preceding study showed very similar trends, so it is possible to apply both type of tank to the developed technology.