The invention discloses a composite enhancing material special for high-performance concrete used for an intermediate-level radioactive waste concrete disposal container and a preparation method of the composite enhancing material. The composite enhancing material comprises the following components, by weight percentage, 40-60% of slag fine powder, 10-40% of coal ash, 15-30% of silica fume, and 1-2.5% of carbon fiber. Different additives develop different optimizing function on working performance, mechanical property and endurance capacity of high-strength concrete, and short carbon fiber can improve the cracking phenomenon of the high-strength concrete, so that a product meeting requirements of high cracking resistance and high durability of a disposal container concrete material is obtained. In an actual production process, a composite enhancing material special for manufacturing a concrete container is provided and is beneficial for metering control. The production cost is reduced, and the production efficiency is improved.