Abstract: In order to study the motion responses and section loads of one new type floating trestle bridge (FTB), and to explore the difference of the motion responses and section loads of the FTB with different lengths, the three-dimensional hydroelasticity theory was used to analyze the hydroelastic responses of the FTB. Obtained are the principal coordinate responses of different FTBs under different wave directions and different wave lengths, and calculated are the motion responses at the center of gravity of the bridge pontoon, the vertical displacement of each node of the central axis of the deck, and the vertical bending moments as well as vertical shear forces of key sections. The analysis results show that the principal coordinate responses of rigid modes calculated by the present method are consistent with the results calculated by software AQWA, and that the motion responses of the pontoons calculated by the present method are in a good agreement with the model test results. The elastic distortion has a certain influence on the motion responses of each node, and as the number of bridge pontoons increases and the length of the FTB increases, the influence of elastic distortion on the vertical displacement of each node becomes more and more significant; and the section loads increase with the increase of the length of the FTB, especially for the peak values of the vertical bending moment.