Abstract: To study the acid value of tea polyphenols dietary supplement by potassium hydroxide titration.The contents of the capsule were extracted with petroleum ether,the solution was collected and evaporated in a water bath of less than 60 degrees centigrade.Weigh the residue quantitatively,dissolve it in ether-ethanol mixture,add a bromothymol blue indicator,and shake it with 20ml saturated sodium chloride solution.It's potassium hydroxide blue.At the same time,a blank experiment was carried out.The content of acid value was calculated and the relative standard deviation was calculated.The RSD does not exceed 15%when the acid value is less than 1 mg/g,and does not exceed 12%when the acid value is greater than or equal to 1 mg/g.The titrimetric method for determination of acid value in tea polyphenols dietary supplement is simple,accurate,stable and practical,which provides technical support for the formulation of relevant standards.