In this paper,UV-Visible spectrometry was employed to study the ionization constant of scutellarin.The standard solution of series pH value were prepared and the absorbance was measured at suitable wavelenths.Then the ionization constant is obtained according to the change of absorbance.The first dissociation constant was 8.52 when 368 nm was selected as the analytical wave length;The second dissociation constant was determined to be 11.20 using 365 nm as the analytical wave length;The third dissociation constant was 12.56 using 326 nm.This way is proved to be simple,applicable and easily operated.