Abstract: An L-arabinose is prepared through the following processes: (1) dissolving L-arabinose starting material in water, adding activated carbon, filtering, and removing the activated carbon to give a clear filtered sugar liquid; and (2) subjecting 40-55% (v %) of the clear filtered sugar liquid obtained in step (1) to evaporation until sugar degree reaches 55-65% Brix, adding the remaining clear filtered sugar liquid in a fed-batch manner after adding a proper amount of the L-arabinose starting material as seed crystal, and continuing concentration after the fed-batch addition is completed. The process of preparing the arabinose and the preparation thereof does not involve addition of any auxiliary material nor complicated granulation processes. The obtain product can be directly applied as a bowel cleanser drug. The range of particle size is controllable.