According to the requirements of processing, testing and lifting of a 2.7m spherical mirror, an inspection device for support testing, posture adjustment and turnover of mirror body is designed, which can meet the requirements of the support accuracy of the knife edge instrument in the rough polishing stage, the posture adjustment requirements in the mirror body test, and the overturning requirements of the mirror body back structure processing and assembly. For different working conditions, the stiffness and strength are analyzed, the force model of the mirror body under various working conditions is established, and the supporting accuracy, stiffness and stress of the mirror body are analyzed. The results show that the mechanical structure of the device meets the requirements of strength and stiffness; the support stress of the mirror body is less than 1MPa under various working conditions, which is less than the required stress of microcrystalline; the accuracy RMS of the mirror body with the sling side support is 14.15nm, which meets the measurement accuracy requirements of rough polishing stage.