A measurement method of the particle-based reflective display is proposed, estimated, and compared with reported method. The reflectivity measurement by previous studies is simply obtained by integrating sphere, but it has a limitation for the estimation of real moving particles because its data include surface reflection and incomplete attachment on electrodes. To get the number of real moving particles, the area by attached particles on the electrodes is calculated at microscopic signals. The moving particles on subthreshold voltage are observed and this fluctuational variation of surface on subthreshold voltage gives a tip to understand the driving mechanism. By this measurement we ascertained the relationship of a particle layer and real driving particles, and the feasibility of observation and estimation for moving color particles, which were measured by the reflectivity and CIE (Commission Internationale de I`Eclairage) system of color specification at previous studies.