Abstract: Acid precipitation properties of rice and wheat straw waste liquor under variety pH value(composition of precipitation and COD of waste liquor)were studied in this paper,the properties of lignin graded were analyzed.Results indicate that pH value is the main factor which affects the acid precipitate process.When pH is over 6,only a little precipitator can be obtained,and the main component is ash.So,highpurified lignin obtained has good applied properties by classification.This study can guide the process of acid precipitation and utilization of precipitated alkali lignin.