The paper aims to extract saponins from Ardisia mamillata by polyethylene glycol (PEG)-ammonium sulfate (NH4)2SO4 two-phase system to study the stability of saponin. The effects of water bath time, temperature, PEG average molecular weight, PEG mass fraction, (NH4)2SO4 mass fraction and pH on the extraction efficiency were observed with the extraction rate of saponins in the system as index. The optimum extraction conditions were optimized by response surface methods, and the stability was studied. The results showed that the water bath time was 40 minutes and the temperature was 70 ℃, PEG600 mass fraction, (NH4)2SO4 mass fraction and pH was 25.0%, 21% and 6.20, respectively. Under these conditions, the extraction rate of saponins was 4.73%. Ardisia mamillata saponins was suitable for preservation at temperatures below 20 ℃ and pH 6. The establishment of this system can effectively extract saponins from Ardisia mamillata and provide reference for its follow-up study.