The invention relates to a sand preparing method for a soil test. The sand preparing method comprises the following steps of: setting a barrel body of a sand preparing device, the height from a shower nozzle to a sand surface, the hole diameter of a screen and the shifting path and speed of the shower nozzle; preparing a sand sample, and calculating the relative compaction of the sand sample; respectively independently changing the height from the shower nozzle to the sand surface and the size of the hole diameter of the screen, preparing a sand sample I again, and calculating the relative compaction of the sand sample I; making a relational graph of the relative compaction of sand and the height from the shower nozzle to the sand surface and the hole diameter of the screen; finding out the relative compaction of the corresponding sand and the distance from the shower nozzle to the sand surface from the relational graph according to the relative compaction of the required sand; preparing required sand according to the hole diameter and the height of the that the distance from the shower nozzle to the sand surface. Compared with the prior art. The method provided by the invention particularly aims to the preparation of the sand sample in the soil test, the disadvantage of the traditional method is recovered, the sample which is uniform and can meet a requirement is accurately prepared, and the sample has repeatability, so that the consistency of the test sand sample is guaranteed.