Abstract: This study investigated the co-fermentation of shrimp shells/heads and soybean substrates using a Mucor, Rhizopus oryzae, and Aspergillus oryzae mixed culture system. The microbial ratio was optimized through orthogonal experiments, with amino nitrogen content and sensory attributes serving as key assessment criteria. The optimal fermentation conditions were further validated by volatile flavor analysis. Additionally, the quality of laboratory-produced shrimp paste was compared with commercial products based on color parameters, total volatile basic nitrogen, pH, and free amino acid composition. An optimal inoculum ratio of 3:1:3 (Mucor:Rhizopus oryzae:Aspergillus oryzae) yielded shrimp paste with 1.19 g/100 g amino nitrogen and a 92.53-point sensory score. Key aromatic compounds, including pentanal (monomer/dimer), hexanal, 3-pentanone, 3,5,5-trimethyl-2-cyclohexen-1-one, and ethyl acetate, demonstrated superior relative odor activity values. Compared with them to commercial counterparts, our formulation exhibited enhanced color parameters (a^*=12.26, b^*=19.91), lower total volatile basic nitrogen (117.98 mg/100 g), a higher proportion of umami amino acids (20.78% of total amino acids), and a lower proportion of bitter amino acids (42.77% of total amino acids). Fourier-transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy analyses confirmed that the proteins in the shrimp byproducts were fully utilized during fermentation, with the remaining insoluble fractions exhibiting the characteristic functional groups, crystalline structure, and microscopic morphology of α-chitin. The findings of this study demonstrate that mixed-strain fermentation enhances flavor characteristics while reducing the accumulation of undesirable metabolites, providing both a theoretical foundation and technical support for the value-added utilization of shrimp by-products and industrial-scale production of premium shrimp paste.