The present invention provides a method for preparing standardized serum mixture for determining allergen potency which comprises: 1) providing multiple serum samples from patients moderately hypersensitive to said allergen; 2) determining the relative content of sIgE against said allergen in each serum sample, obtaining the mean value of the relative content of sIgE of said multiple serum samples, and obtaining deviation value of the relative content of sIgE of each serum with respect to said mean value; 3) removing at least 5% of serum samples that have the largest and smallest deviation values respectively, and mixing the residual sera at the same volume. The invention also relates to the serum mixture prepared by the method as well as the use of such serum mixture.