The invention discloses a preparation system and a preparation method of high-purity food-grade liquid carbon dioxide, and solves the problems of low purity of carbon dioxide, insufficient energy utilization and high production cost in the prior art. The system disclosed by the invention comprises a hybrid compression system, a desulfurization catalytic combustion system, a dry filtration system and a purification system; the hybrid compression system comprises a vaporizer, a preheater, a raw gas mixing tank, a compressor and an air temperature vaporizer; the desulfurization catalytic combustion system comprises a heat exchanger, an electric heater, a desulfurization tower and a catalytic reactor, and the dry filtration system comprises a water cooler, a drying tower and a filter; and thepurification system comprises a purification tower, a feed pump, a first gas-liquid separator, a liquefier and a second gas-liquid separator. Liquid industrial-grade carbon dioxide is vaporized and mixed with oxygen, and then compressed, desulfurized and combusted, cooled and dried, and then subjected to gas-liquid separation, and liquid is purified to obtain food-grade liquid carbon dioxide afterbeing separated. The preparation system disclosed by the invention is simple in structure, low in production cost and high in recovery rate.