As a key mechanical property index of materials, hardness directly affects the service performance, operational safety, service life and comprehensive quality of core products in advanced manufacturing fields including aerospace, high-end equipment, precision instruments and the automotive industry. Given the inherent drawbacks of traditional laboratory hardness testing, such as random sampling, delayed data feedback and independent data silos, this paper proposes and develops a digital on-line Brinell hardness testing method for complex components represented by aero-engine blades. The proposed method overcomes key technical bottlenecks, including precise positioning of irregular workpieces under dynamic conditions, adaptive constant-force surface grinding, and high-precision recognition of low-quality industrial indentation images. Relying on the above technologies, a digital on-line hardness testing production line is constructed, which supports full-coverage hardness data collection and real-time traceable result evaluation. Experimental results show that the established system achieves four times higher testing efficiency, with the GRR% of measurement system analysis (MSA) reaching 17.42%. Long-term industrial application and verification on tens of thousands of workpieces demonstrate the effectiveness and technical advantages of this method in realizing in-situ, real-time, fully automated and traceable hardness quality control. This study provides a viable technical route for promoting the integration of metrology and testing under the background of intelligent manufacturing.