The TAPPI T 401 standard specifies a method for the analysis of fibers in paper and Cardboard. This test is used to identify the types of fibers present in paper or Cardboard samples and to quantitatively estimate them. Analysts need to be proficient in pulp and paper microscope technology and familiar with the morphological characteristics and dyeing reactions of different fibers to ensure the accuracy of the analysis results. By following the TAPPI T 401 standard, manufacturers can understand the fiber composition of their products, optimize the production process and improve the mass of the product. In addition, this method has important significance for mass assessment and reuse of recycled paper products.