Theory and method for the determination of quantum efficiency for photochemical hole buring (PHB) are given in detail. For the organic impurity center tetrahydroxyphenylporphin (THP) imbedded in poly (methylmethacrylate) (PMMA) amorphous matrix, the quantum efficiency is calculated according to the parameters measured at liquid helium temperature. Integrated absorption coefficient instead of dipole moment is used in the calculation.