The invention relates to an ultimate strength test device and method for very large floating structure under bending load, and the device comprises a test platform, wherein both ends of the test platform are respectively installed with a first reaction frame and a second reaction frame, the second reaction frame is installed with an axial loading system by combining a cushion stool and a support beam, a test model is installed between the axial loading system by and the first reaction frame, the axial loading system applies compression load to the test model, and a vertical loading system forapplying bending load for the test model is also included; the method comprises the following steps of making a very large floating structure shrinkage ratio test model according to the scale ratio, performing verification by numerical simulation, performing compression and bending on the shrinkage ratio test model and the test under bending combined loading effect on the test device to obtain test data such as strain, deformation, limit load and end displacement, thereby obtaining the ultimate strength condition of prototype by backward reasoning according to the scale ratio. The ultimate strength test device and method for very large floating structure under bending load provided by the invention provide research basis and reliable technical support for the structural design and optimaldesign of the very large floating structure.