With the development of non-destructive and micro-destructive testing technologies, micro-analysis of paper used in archives has been increasingly applied. At present, the most commonly-used method for paper fiber observation and detection is the staining method in conjunction with optical microscopy; however, this method depends greatly on the quality of staining agents. Polarized light microscopy can be used without staining fibers and thus provides a better way for fiber identification from the perspective of fiber morphological characteristics. By reviewing the related research on the application of polarized light microscopy in the detection and analysis of paper, it is found that the current research on the fiber detection of paper by this technology is still in the stage of theoretical analysis and lacks practical applications. Observation and analysis of the fiber morphology and other components of paper used in Mustang archives using polarized light microscopy illustrate the effective application and the unique advantages of this method for the observation and identification of paper fibers used in archives and for the distinguishment between fibers and other cells or crystals in papermaking pulp.