The invention discloses a soil conditioner for preventing soil hardening. The soil conditioner is prepared from the following raw materials: rice husks, wheat hulls, banana fiber, cocoanut fiber, barks, turf, leguminous plant straws, bean cakes, vinasse, coffee residues, rape seed cakes, cottonseed cakes, fish meal, bone meal, medical stone powder, zeolite powder, bentonite, urea, ammonium sulfate, monopotassium phosphate, ferrous sulfate, magnesium sulfate, zinc sulfate, potassium chloride, calcium superphosphate, calcium peroxide, magnesium peroxide, borax, an agricultural water-retaining agent and a microbial agent. The invention further provides a preparation method of the soil conditioner for preventing soil hardening. The soil conditioner disclosed by the invention is low in raw material cost and scientific in component, and can well adjust the soil structure and prevent the soil hardening.