The invention relates to a non-contact precise tool setting gauge of an ultra-precise diamond turning tool and a tool setting method. The tool setting gauge comprises a supporting ring body, lenses inthe X direction and the Y direction, CCDs and a lighting source in the X direction. The lens in the X direction and the CCD of the lens in the X direction are arranged at the position, correspondingto the X-axis direction of the lathe coordinates, of the supporting ring body, the lens in the Y direction and the CCD of the lens in the Y direction are arranged at the position, corresponding to theY-axis direction of the lathe coordinates, of the supporting ring body, the lenses in the X direction and the Y direction are located on the inner side of the supporting ring body, the CCDs in the Xdirection and the Y direction are located on the outer side of the supporting ring body, and the lighting source is arranged at the position, facing the lens in the X direction, of the inner side of the supporting ring body. The tool setting gauge and the tool setting method thereof replace a traditional trial cutting method, ultra-precise machining tool high-precision optical online detection isachieved, the problems that an ultra-precise machining tool is long in position adjusting period, and tool wear is hard to avoid are solved, machining efficiency is greatly improved, the tool is freeof wear, and the wide application prospects and the large popularization value are achieved.