A progressive iterative optimization strategy was used to systematically optimize the traditional nine-steaming and nine-drying process of Polygonatum sibiricum to elucidate the dynamic changes in the sensory quality， the content of active substances and the effects of polysaccharides on the immunomodulation during the process and reveal the scientific basis of the nine-steaming and nine-drying technology. The results showed that the four-steaming and four-drying of Polygonatum sibiricum had the optimal sensory profile， and further processing led to a decrease in the flavor and texture. The content of ethanol-soluble extractives decreased gradually from 85.91% in the raw sample to 63.50% and the content of polysaccharide decreased from 9.86% to 3.13% in the product of nine-steaming and nine-drying with the increase in the cycles of processing， while the content of total saponins， flavonoids and total phenols was 5.18， 14.46， and 100 times of that in the raw materials， respectively. The results of experiments in mice showed that the crude polysaccharides extracted at various stages of processing enhanced the immune function of immunosuppressed mice， with most groups processed outperforming the positive control. Among which， polysaccharides from the processed group with four-cycle had the most potent effects of immunomodulation in mice， effectively restoring the microstructural integrity of the spleen and thymus， with the indexes of organ， the content of serum cytokines（IL-2，IFN-γ） and immunoglobulin（IgA， IgM） significantly better than that in the raw product and the nine-cycle group. It is indicated that the mechanism of the nine-steaming and nine-drying technology of Polygonatum sibiricum results from multiple dimensions including sensory quality， active components and immunomodulation of polysaccharides. It will provide a scientific basis for standardizing the technique of processing to improve the quality and the rational utlization of Polygonatum sibiricum.