Abstract: Based on the sensitive characteristics of nitrogen-vacancy (NV) color center to magnetic field, the diamond quantum sensor containing a concentration of 1-2 ppm NV color center was the core, and the quantum spin of the NV color center excited by microwave resonance frequency sweep was the foundation, and the NV color center was excited by the optimized confocal optical path to collect the reflected optical signal containing magnetic field information for signal collection, and the control acquisition module composed of three boards was used to filter and visualize the signal for signal processing, and a quantum precision measurement system was built. The quantum precision measurement system was used to detect metal cracks at a depth of 0.1 mm-1 mm and a lifting value of 5 mm-15 mm. The experimental results showed that the sensitivity of the system was 6 nT · $\sqrt{Hz}$^-1, the minimum depth of 0.1 mm and metal crack detection with a maximum lift value of 15 mm can be achieved, providing a new detection method for metal crack industrial detection.