Replacing highly reflective envelope materials, retro-reflective materials (RRMs) used as building coatings can help to fight the urban heat island effect. The common component of RRMs are mainly glass beads and prisms. The use of glass beads is relatively wider. This paper presents a study on the reflective principle of a single glass bead. Retro-reflective directional characteristics of a glass bead were evaluated by simulation. It showed that the reflective directional characteristics of glass beads are different for different refractive index of glass beads. Among the 3 refractive indexes evaluated, the retro-reflective directional characteristics of glass beads are the most remarkable when the index is 1.93. Compared to the refractive index of 1.93, both a lower refractive index and a higher refractive index have a much wider reflective distribution on the glass bead surface. The reflective directional properties are affected by the refractive index of the glass bead, but almost unaffected by the angle and direction of the incident light.