An XRF device has been adopted to study the whole-area componential distribution of the pigments in the oil painting “Lady in Evening Dress” created in 1955, and the material information of the pigments of this oil painting is analyzed. The major pigments used in this painting created in the middle of the 20th century are still mineral pigments. In addition, organic pigments were also applied in a small number of areas in the painting, and the pigments in some parts are non-standard oil paints prepared by the painter himself. Due to the artistic characteristics of the oil painting, the componential content of some areas with similar colors is the same; however, there are a few areas with large fluctuations. Therefore, the components of a specific area can be regarded as the unique fingerprint information to provide a basis for its identification.