To address the inherent limitations of traditional laboratory hardness testing methods, such as random sampling, result latency, and data silos, this paper proposes a digital online Brinell hardness testing method tailored for complex components, exemplified by aero-engine blades. The proposed method overcomes critical technical bottlenecks, including the precise positioning of irregular workpieces under dynamic conditions, adaptive constant-force surface grinding, and the high-precision recognition of low-quality indentation images in industrial environments. Consequently, a digital online testing production line was established, enabling accurate hardness measurement, real-time result evaluation, and full data traceability. Experimental results demonstrate that compared to traditional methods, the proposed approach increases measurement efficiency by a factor of four. Furthermore, the Measurement Systems Analysis (MSA) yielded a Gauge Repeatability and Reproducibility percentage (GR&R%) of 17.42%, with long-term operational performance consistently meeting requirements. By facilitating in-situ, real-time, fully automated, and traceable hardness measurement, this method provides a viable technical pathway for achieving the "integration of metrology and testing" within the context of intelligent manufacturing.