This paper mainly studied the method of ammonium sulfate precipitation,which could preliminary purify the limit dextrinase.Crude enzyme extracts from barley malt were purified by gradient ammonium sulfate salting,and the salting out curve was settled soon after.Accordingly,the preliminary purification method of ammonium sulfate salting was determined by salting out curve.In this paper,the influence of purity and yield of the limit dextrinase was studied for three methods of salting which were employed to purify limit dexrtinase.The results showed that it had two enzyme activity peaks in salting out curve at 35% and 80% saturation,but saturation of 80% could salt out most of the enzyme protein.We precipitated enzyme protein by one-step(80% saturation),two-step(25% and 80% saturation) and three-step(25%,35% and 80% saturation) method,respectively.Wherein the three-step method could make the purity(A510/A280) of limit dextrinase up to 1.635,and the purification fold and yield was 8.8 and 49.5%,respectively.The results showed that the three-step(25%,35% and 80% saturation) salting was a better method to obtain high purity of limit dextrinase.This study is groundwork for further purification of limit dextrinase.