The invention discloses a fracturing ball of a double-layer structure used for fracturing an oil and gas well and a preparation method thereof.The fracturing ball comprises a basal body made by hard high polymer and an elastomer material layer covering the basal body. Preferably, the basal body is largely composed of a high-strength high temperature-resistant thermoplast. The elastomer material layer is composed of elastomers suitable for the environment of fracturing fluids. The fracturing ball of the double-layer structure used for fracturing the oil and gas well and the preparation method thereof have following beneficial effects: the fracturing ball is large in selectable proportion range, low in requirement for machining precision and fine in pressure-maintaining effect for sealing; due to the double-layer structure comprising a highly-elastic outer layer and a hard core, sealing effect can be improved and the possibility of damage to the fracturing ball because of stress concentration of a local region is decreased so that occurrences of failure for the fracturing ball under the well are greatly reduced; reliability of multi-layer fracturing supporting equipment is effectively enhanced; and the fracturing ball is simple in preparation technology, easy in control and low in cost.