Ultraviolet organic light-emitting devices (UVOLEDs) may combine the tunability properties of organic materials through modifying the molecular structure and the advantages such as large-area, low-cost, and facile to realize high-performance UV sources. In the state-of-the-art UVOLEDs, the external quantum efficiencies (EQE) are more than 3%, but only a few have achieved pure UV emission and could not compromise the durability and irradiance at the same time. Portable compact UV sources with a narrow band made significant achievements in biomedical science and forensic appraisal. The microcavity effect is useful for achieving the desired narrow peak emission. In this study, asymmetric structural design with a specific distributed Bragg reflector (DBR) structure was employed to achieve narrow-band pure UV emission microcavity UVOLEDs (μC UVOLEDs). These μC UVOLEDs can realize tunable wavelength from 366 to 400 nm, with a full width at half maximum (FWHM) of 9.95-15.2 nm and a maximum irradiance of 2.79-5.63 mW/cm. Also, the durability of the μC UVOLED has been considered, which presents a lifetime of 63.2 h under an irradiance of 0.016 mW/cm. Moreover, the ability to identify 100 RMB with an efficient μC UVOLED has also been demonstrated. This investigation not only demonstrates the encouraging potential of narrow-band pure UVOLEDs but also provides a feasible strategy for the optimal design of μC UVOLEDs by utilizing the asymmetric structure.