In response to the lack of clarity around the variation pattern of physicochemical quality and the challenges in precise regulation of process parameters during the processing of stewed Polygonatum sibiricum Delar. ex Redoute (SPR), this study systematically analyzed the quality evolution during the stewing process and established fitting curves between quality attributes and key processing parameters, aiming to provide a reference for process optimization. Samples were collected from seven major processing stages: rinsing, deep stewing, light drying, wine processing, tiger stewing (intense stewing), continued drying, and baking. The samples were subjected to qualitative and quantitative analyses of color, texture, and compositional indicators, including sugars, proteins, total flavonoids, 5-hydroxymethylfurfural (5-HMF), and 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP), and a model to predict the optimal parameters was established based on the correlation between quality changes and processing parameters. The results showed that the color and texture of SPR changed significantly before and after deep stewing: the color turned from yellowish-white to dark brown, and the texture became soft and sticky. Moreover, boiling time was identified as a key process parameter to control during the deep stewing stage. In addition, this study found that the contents of various substances in SPR, such as sugars and proteins, changed significantly. Correlation analysis suggested that the contents of DDMP, 5-HMF, polygonatine A, free sugars, and total flavonoids were the major material basis for the changes in color and texture. The proposed prediction model provides theoretical and technical support for the establishment of a standardized stewing process for P. sibiricum Delar. ex Redoute.