This standard specifies a method for evaluating the characteristics of pulp fibers, with its core involving the use of a Bauer-McNett fiber classifier to screen a pulp suspension. The principle is as follows: dispersed pulp is introduced into a series of step-arranged screening containers, where fibers of different lengths are retained on screens of corresponding mesh sizes by water flow. Finally, the oven-dry mass of fibers retained on each screen plate is weighed, and their mass percentage relative to the total input is calculated. This method is applicable to various types of pulp used in papermaking and serves as a fundamental test for analyzing fiber length distribution and evaluating papermaking performance. Key auxiliary equipment required to complete the test includes a standard fiber disintegrator for pulp pretreatment, as well as an oven and analytical balance for drying and weighing.