The invention relates to a method for preparing a green high-efficiency soil conditioner, which belongs to the technical field of conditioner preparation. According to the invention, substances such as bentonite and fly ash are mixed, a mixture is applied to the irrigated paddy field, water dropwort is planted in the paddy field, and loach can be cultured in the paddy field, after the water dropwort grows to a certain height, the water dropwort is cut and the loach is removed, the paddy field after the water is discharged is insolated, and the soil on the surface of the paddy field is collected, the black powder is obtained through drying and crushing processes, polished rice and glutinous rice are taken as the raw materials for fermentation to obtain a precipitate slurry, and the precipitate slurry is mixed with the black powder to obtain the product. The green high-efficiency soil conditioner does not contain heavy metal, cannot generate harm on soil ecology, increases the output and quality of an agricultural product; has the effects of water retention, fertility increasing and ventilating effects, the water-holding capacity is increased by 15.6-25.3%, the unit weight of the soil is reduced by 0.04-0.05 g/cm<3>, and the agricultural product output can be obviously increased.