A detection method for identifying the substances in a to-be-detected mixture of different substances soluble in the same solvent, the method comprises the following steps: a) performing measurement spectrum line collection on a solution prepared by mixing at least one different standard sample substance with a first calibration substance, in equal proportions, wherein the first calibration substance is the solvent of the solution, and storing the measurement spectrum in a storage module; b) selecting a characteristic peak of the measurement spectrum line for each of the at least one standard sample substance; obtaining an intensity value of the characteristic peak of the at least one standard sample substance; and constructing a relative activity database with the relative activity L of the at least one standard sample substance by c) calculating the relative activity L of the at least one standard sample substance according to L = a ∗ b, wherein a is a constant and b is a ratio of an intensity peak value of the measurement spectrum line of the standard sample substance to the intensity peak value of the measurement spectrum line of the first calibration substance; obtaining the relative activity of each standard sample substance by repeating, for each standard sample substance, the preceding steps a) to c), and adding the relating activity of each standard sample substance to the relative activity database; performing measurement spectrum line collection on the mixture of different substances to be identified, dissolved in the first calibration substance, and setting the constant a as a=1, obtaining an intensity value of each of the characteristic peaks of the measurement spectrum, querying the relative activity database L to obtain relative activity of each substance in the mixture, and determining the proportion contents of the different substances contained in the mixture from the peak intensity ratio and the relative activity established in the database. a) performing measurement spectrum line collection on a solution prepared by mixing at least one different standard sample substance with a first calibration substance, in equal proportions, wherein the first calibration substance is the solvent of the solution, and storing the measurement spectrum in a storage module; b) selecting a characteristic peak of the measurement spectrum line for each of the at least one standard sample substance; obtaining an intensity value of the characteristic peak of the at least one standard sample substance; and constructing a relative activity database with the relative activity L of the at least one standard sample substance by c) calculating the relative activity L of the at least one standard sample substance according to L = a ∗ b, wherein a is a constant and b is a ratio of an intensity peak value of the measurement spectrum line of the standard sample substance to the intensity peak value of the measurement spectrum line of the first calibration substance; obtaining the relative activity of each standard sample substance by repeating, for each standard sample substance, the preceding steps a) to c), and adding the relating activity of each standard sample substance to the relative activity database; performing measurement spectrum line collection on the mixture of different substances to be identified, dissolved in the first calibration substance, and setting the constant a as a=1, obtaining an intensity value of each of the characteristic peaks of the measurement spectrum, querying the relative activity database L to obtain relative activity of each substance in the mixture, and determining the proportion contents of the different substances contained in the mixture from the peak intensity ratio and the relative activity established in the database.