The invention discloses a flexible thin-wall bearing test mounting shaft assembly. The flexible thin-wall bearing test mounting shaft assembly comprises a pull nail, a bearing mounting body and flexible thin-wall bearing clamping devices; the bearing mounting body comprises a shaft main body, an oval shaft neck for achieving radial positioning of a flexible thin-wall bearing is arranged on the front portion of the shaft main body, a conical portion is arranged on the rear portion of the shaft main body, the pull nail is arranged at the tail end of the oval conical portion in a connected manner, and the flexible thin-wall bearing clamping devices are detachably and fixedly arranged on the two sides of the oval shaft neck and are used for achieving axial positioning of the flexible thin-wall bearing; fixing of the flexible thin-wall bearing on the bearing mounting body is achieved, and the flexible thin-wall bearing test mounting shaft assembly is formed, a dynamic balance structure during high-speed rotation of the bearing mounting body is ensured, and the assembly is particularly suitable for simulating the actual condition of oval deformation of the flexible thin-wall bearing in a harmonic reducer, can be connected with a high-speed electric spindle, is compact in structure, rapid and convenient to mount and dismount, and safe and reliable in work and can improve the accuracy of the test result.