Abstract: The identification and traceability of Apocynum venetum have long been plagued by two major problems. First, Apocynum venetum is extremely similar in appearance and infrared spectrum to flax and other fiber plants, leading to insufficient discrimination by traditional methods. Second, the processing process significantly alters the material composition of Apocynum venetum, causing interference in traceability. This study takes Apocynum venetum products at different processing stages as the research object, with flax as the control sample, and uses an elemental analyzer-isotope ratio mass spectrometer (EA-IRMS) to accurately determine their carbon stable isotopes (δ¹³C), hydrogen stable isotopes (δD), and oxygen stable isotopes (δ¹⁸O). It also combines multiple statistical methods such as principal component analysis (PCA), cluster analysis, and partial least squares discriminant analysis (PLS-DA) for data interpretation. The research shows that flax from different origins (such as Xinjiang and France) presents unique isotopic fingerprints, which not only effectively distinguishes processing methods and blending situations but also accurately traces the raw material species and origin. This paper systematically compares the isotopic variation patterns of Apocynum venetum under different processing techniques, confirming that stable isotope technology can effectively distinguish Apocynum venetum and its products, identify processing methods, and trace the origin of raw materials, providing a new technical approach and key data support for the scientific traceability and authenticity identification of natural textiles.