As for the problem of long machining and measurement iteration cycle of metal reflectors by the single point diamond turning, the fringe reflection method with a large dynamic range and fast detection speed is introduced, and the on-machine surface measurement of metal reflectors is realized, which improves the manufacturing efficiency. The mechanism of surface shape measurement based on fringe reflection is investigated. By the ray tracing program, the simulation is conducted as for the reflector surface with an aperture of 100 mm and the micron-sized requirement of position calibration in the fringe reflection on-machine surface shape measurement system is analyzed. The on-machine measurement of concave spherical metal reflectors with an aperture of 100 mm is carried out, and the measurement precision is superior to 1 μm. This research provides a certain reference for the machining of reflector by the single point diamond turning.