This guide describes a method for measuring the roundness of Glass beads in pavement marking systems using a flow digital image analyzer. The roundness of Glass beads is critical to the reflection performance of pavement marking. This guide provides a standard method for measuring the roundness of Glass beads, ensuring that it meets the specification requirements for pavement marking. The measurement results can be used to evaluate and optimize the mass of Glass beads to improve the performance of marking systems. While this method also has potential in Miscellaneous industrial applications, this guide is primarily used for roundness measurement in the field of pavement marking.