A method for preparing volcanic rock soil, and the volcanic rock soil prepared by the method are provided to improve the efficiency of the volcanic rock soil for air purification effect and plant growth promotion effect when applied to flowering grass. A method for preparing volcanic rock soil comprises the steps of (10) pulverizing volcanic rock by a certain size; (20) polishing the surface of the pulverized volcanic rock to obtain the volcanic rock by-product; (110) heating the volcanic rock by-product generated at the polishing step to remove the impurities and microorganism; (120) washing the heated volcanic rock by-product; and (130) drying the washed volcanic rock by-product.
