In order to realize the accurate description of the extraction process of continuous countercurrent extraction (CCE) for Astragalus polysaccharides, a mathematical model of diffusion and backmixing was established and solved. The two-phase solute distribution in the single-flow continuous countercurrent extractor was described. The scale for describing the pilot scale was established. The diffusion back-mixing numerical model of the two-phase solute distribution in the extractor was tested by multi-effect simulation CCE of Astragalus polysaccharides. The results showed that the extraction temperature was 40~70 ℃, and the solid-liquid ratio was 1：6~1：14 (g/mL), within the single factor variation range of extraction time 40~70 min, the relative error between the model prediction distribution and the actual sample concentration is controlled ≤15%, which has certain practical value. The model can realize the achieve prediction of the concentration of the two phases in the extraction process of CCE under steady state conditions.