With the increasingly serious electromagnetic environment pollution, electromagnetic shielding materials play a significant role in the information industry. We propose a technique for surface defect characterization of micron diamond particles based on nitrogen vacancy color centers to meet the needs of high-resolution microwave leakage measurement of shielding materials. A micron-sized diamond crystal fixed at the end of a tapered optical fiber is excited with a 532 nm laser, and the red fluorescence emitted by the diamond is collected with an APD, which is modulated by a frequency resonant microwave field. By measuring the fluorescence intensity, the microwave B-field can be inferred. We prepared a split ring resonator to provide the microwave field and a shielding film to cover the surface. Using our system, micron electromagnetic leakage can be observed. Anomalous changes in microwave field intensity were evident in the region where the film leaked. In addition, we also explored the variation of the distance between the probe and the SRR antenna on the microwave field intensity, which increased as the probe got closer to the antenna surface.