Taking the parallel arrangement for example,we study the motion responses and transmission coefficients of pontoon-type floating breakwater under large tidal ranges by laboratory model tests.The results show that the value of transmission coefficients with relative width for the high tide is different from the other tide levels.By a comprehensive consideration of motion responses and transmission coefficients,we give suggestions on the relative width design of floating breakwater.In addition,based on the comparison study on motion responses and transmission coefficients under the same wave conditions of floating breakwaters with different mooring configurations,we point out that the parallel arrangement is more suitable for the water with large tide ranges.The research result may serve as reference for the engineering practice.