The invention relates to a method for the determination of crocetin and its derivative amounts and the derivative composition from gardenia yellow. The method mainly comprises of following steps: the absorbance measurement of a gardenia yellow aqueous solution at known concentration by UV-VIS, the absorption coefficient measurement of total crocetin derivative, the total crocetin derivative amount calculation according to Lambert-Beer law, the relative amount calculation of each crocetin derivative from its absorption coefficient and peak area on HPLC, the amount calculation of each crocetin derivative from the total amount of crocetin derivative and the relative amount of each crocetin derivative, and finally total crocetin amount calculation. In practice, the absorption coefficient of each crocetin derivative is calculated from that of its root structure, crocetin, based on the negative correlation-ship of absorbance with molecular mass of the molecule while the molecular mass of each crocetin derivative is substituted by the m/z value of its parent ion.