Abstract: Objectives: In this study, we investigated how incorporating black soybean-whey blended protein affect the quality characteristics of quinoa semi-dry noodles. Furthermore, we explored the underlying mechanism by which blended protein modulate the properties of semi-dry noodles, aiming to provide a theoretical basis for the development of blended protein staple foods. Methods: We formulated quinoa semi-dry noodles containing various blended protein levels, and evaluated their quality characteristics including cooking properties, texture profiles, colorimetric parameters, in vitro digestibility, and sensory attributes. We assessed the modulation mechanism of the blended protein affecting noodle characteristics using scanning electron microscopy, Fourier transform infrared spectroscopy, and differential scanning calorimetry. Results: B-WP supplementation prolonged the optimal cooking time of quinoa semi-dry noodles and significantly increased the water absorption rate (P<0.05). The cooking loss rate reached the lowest value (5.42%) in the 7.5%B-WP addition group, which was 11.0% lower than that in the 0%B-WP addition group (6.09%). Meanwhile, the blended protein improved the texture profile of the semi-dry noodles. The hardness and cohesiveness of the quinoa semi-dry noodles in the 2.5% B-WP addition group both reached a maximum value (i.e., 42.77 N and 0.26, respectively). The addition of B-WP significantly reduced the degree of swelling (P<0.05). Compared with the semi-dry noodles without B-WP supplementation, the swelling degree of the semi-dry noodles with 7.5% added B-WP decreased by 23.06%. B-WP supplementation enhanced the hydrogen bond strength within the quinoa semi-dry flour and improved starch orderliness. The microscopic structure results revealed fewer pores and more cross-linked network structures. Meanwhile, the in vitro digestion test indicated that the starch hydrolysis rate and expected glycemic index (eGI) of the B-WP-supplemented quinoa semi-dry flour significantly decreased (P<0.05), with the glycemic index decreasing from 77.75 in the 0% B-WP addition group to 59.43 in the 7.5% B-WP addition group. The sensory scores of the quinoa semi-dry flours with 2.5%~10% B-WP addition were better than those of the 0% B-WP addition group. Conclusions: Quinoa semi-dry noodles with 7.5%B-WP supplementation demonstrated optimal cooking properties and textural characteristics, achieving the lowest expected glycemic index (eGI) and highest sensory evaluation scores. Mechanistically, blended protein fortification reinforced the internal gluten network, enhanced protein-starch crosslinking, and reduced starch leaching. This concurrently promoted starch molecular ordering and limited enzymatic accessibility, ultimately suppressing starch hydrolysis rates while improving the overall product quality.