Ginsenoside Rg5 is a conversion product of the protopanaxadiol saponin (PPD), exhibiting good pharmacological activities such as anticancer, anti-inflammatory, memory improvement, and anti diabetes. Due to its poor stability, ginsenoside Rg5 is commonly prepared employing mild organic acids as catalysts, a practice that may result in diminished reaction rate and yield. This study aims to optimize the process conditions for the preparation of ginsenoside Rg5 catalyzed by hydrochloric acid assisted by high viscosity chitosan, with the objective of enhancing the conversion rate of ginsenoside Rg5 and minimizing its decomposition. The surface response method was employed for the optimization process. The preliminary exploration of the mechanism of action of chitosan was conducted. The experimental findings indicate that the acid concentration of 0.17 mol/L, high viscosity chitosan dosage of 20 mg, reaction temperature of 65 ^oC, and reaction time of 100 min constitute the optimal process for the preparation of ginsenoside Rg5. It was observed that under the optimal conditions, the highest yield of Rg5 achieved 58.92%. The investigation into the adsorption mechanism of high viscosity chitosan reveals that the initial adsorption process involves the binding of hydrogen protons by chitosan, followed by the subsequent adsorption of PPD saponins facilitated by the hydrogen protons. Furthermore, it is observed that high viscosity chitosan exhibits a greater affinity for strongly polar saponins compared to weakly polar saponins. The high viscosity chitosan facilitates the ongoing adsorption of PPD saponins, which possess greater polarity, onto the surface of chitosan. This process leads to the formation of ginsenoside Rg5, which exhibits lower polarity. Subsequently, the generated ginsenoside Rg5 is dissolved in a solution with reduced acid concentration, aiding in the stabilization of Rg5. This sequence of events involving adsorption, conversion, and desorption forms a cycle that enhances the yield and rate of ginsenoside Rg5 preparation.