The invention relates to light-cumulating luminescent size and a preparation method thereof, and the preparation method has the steps as follows: 1) preparing carriers: dissolving polyester resin in a cellosolve to obtain a carrier according to the mass ratio of 1:2-4, and dissolving VMCH in a cellosolve to obtain a carrier B according to the mass ratio of 1:4-8; boosting the temperature to 70-80DEG C in the dissolving process, and stirring while dissolving; and mixing the carrier A and the carrier B according to the ratio of 2-4:1, and preparing to obtain the required carrier; 2) mixing materials: fully mixing long afterglow luminescent materials with the carrier according to a certain ratio, adding a certain amount of dispersant, and fully stirring to balance the concentration; and 3) rolling size: fully rolling the mixed size on a three roller machine to obtain the size with the fineness of 15-100mu m. The powder particles prepared by the preparation method in the invention has more uniform agglomeration and dispersion, and can obtain fully-cumulated energy; and the luminescent size in the invention has high luminescent efficiency, can absorb energy more fully in the same period, can last longer luminescent time in a dark environment, and can be widely used.