The invention belongs to the technical field of construction projects and relates to a sand rain process automatic sander. The sand rain process automatic sander comprises a PLC, servo motors, track guide rails, a sand charging barrel, a hose, nozzles, a sanding cylinder, filter plates and a screen, wherein the PLC is connected with three servo motors, and the servo motors are operated to control the track guide rails in the respective direction to move; the sand charging barrel is suspended at a high part, the sand can flow downwards, and the bottom of the sand charging barrel is connected with the top of the nozzles by virtue of the hose; the bottom of the nozzles are screwed with the sanding cylinder, the filter plates of different sizes are arranged among the nozzles and are used for controlling the flow, and the nozzles are fixedly arranged on the track guide rails; and the screen is arranged at the bottom of the sanding cylinder. According to the sand rain process automatic sander disclosed by the invention, the instrument is easy to operate, the three-dimensional motion is automatically controlled, the manual operation errors are reduced, the prepared sample is high in uniformity and repeatability, the relative compactness range is wide, and most of experimental requirements can be met. Moreover, the sand rain process automatic sander is conveniently applied to large model experiments, particularly a centrifugal model experiment.