The invention relates to an ultra-thin flexible evenly distributed pressure loading device applicable to geomechanical model tests, which comprises an ultra-thin hydraulic oil cylinder thruster and a flexible force transmission cushion layer, wherein a loading oil cylinder is arranged at the center of the hydraulic oil cylinder thruster, a linking flange is arranged at the top part of a piston ofan oil cylinder, and the flexible force transmission cushion layer is arranged at the bottom of the hydraulic oil cylinder thruster. The device can be widely applied in surface loading of various geomechanical model tests, the device is simple in structure, flexible for assembly and convenient for operation, a single loading unit is reasonable in size, a hydraulic oil cylinder is a two-way oil cylinder with an oil inlet and an oil outlet, and loading and unloading can be realized by matching with a hydraulic station and a hydraulic automatic control system; simultaneously, a plurality of loading devices can be combined by different arrangement ways, thereby realizing gradient loading. The device organically integrates the hydraulic oil cylinder, the rigid thruster and the flexible force transmission rubber cushion layer, thereby greatly reducing the loading space, reducing the size of a reaction frame on a model, saving steel for the reaction frame, and leading the applicability to bestronger.