The rare ginsenoside Rg5 was efficiently prepared in the presence of molecular sieves. using the multi-functional improved Soxhlet extractor as extraction tool and ginseng fibrous root powder as raw material, hydrochloric acid as catalyst. The extraction process of ginsenoside Rg5 was optimized through one-factor experiment. The optimum result obtained from one-factor test was as follows: extraction solvent was 30 mL methanol, 4A molecular sieve was 0.3 g, the heating temperature in the extraction barrel was 65 ℃, and extraction time was 4 h. Under the optimized conditions, the extraction yield of total ginsenosides reached 10.2% and the yield of rare ginsenoside Rg5 was 3.20%, which could significantly improve the preparation efficiency of ginsenoside Rg5 compared with the traditional Soxhlet extractor. The method has following characteristics such as high extraction yield and simple operation, which indicated the method could extract Rg5 effectively.