Taking ginseng fibrous root powder (GFRP) as raw material, hydrochloric acid as a catalyst and water-saturated n-butanol as the extraction solvent, respectively, the method of preparation of ginsenoside Rg5 from GFRP at atmospheric pressure by heating reflux was studied. The extraction process of ginsenoside Rg5 was optimized through one-factor experiment and orthogonal experiment, the precision test, stability test, repeatability test and sample recovery test were also carried out. High Performance Liquid Chromatography was applied to determine the content of ginsenoside Rg5 in ginseng fibrous root powder extracts. The optimum result obtained from orthogonal test was as follows: ratio of ginseng fibrous root powder to extraction solvent 1∶20g/mL, acid concentration 0.06mol/L, extraction temperature 70℃ and extraction time 5 h. Under the optimized conditions, the yield of ginsenoside Rg5 was 2.48%. Ginsenoside Rg5 showed good stability in 48 h, and the sample recovery rate was 99.32%～103.70%, RSD was 1.33%. The method has following characteristics such as high extraction yield, simple operation, good reproducibility and short extraction time.