The invention discloses high-density self-compacted concrete and a preparation method. The high-density self-compacted concrete consists of the following components in percentage by mass: 15-32% of a cementing material, 20-35% of aggregates, 20-42% of sand, 3-12% of expanded vermiculite, 0.1-0.8 percentage of a water reducing agent, 0.04-0.5% of a thickening agent, 0.2-1.5% of a thixotropy lubricant, 0.08-0.8% of straw fiber and 10-25% of water. The preparation method comprises the following steps: stirring the cementing material, the straw fiber and the thickening agent needed for preparation for 3-6 minutes, sequentially adding the water, the water reducing agent and the thixotropy lubricant needed for preparation, and continuously stirring the mixture for 5-10 minutes so as to obtain a slurry mixed material; B, adding the aggregates, the sand and the expanded vermiculite into the slurry mixed material obtained in the step A, and stirring the mixture for 3-6 minutes, thereby obtaining the high-density self-compacted concrete. By adopting the high-density self-compacted concrete, properties of concrete can be effectively improved, a mixture can be relatively good in flowability and caking properties, and the high-density self-compacted concrete has the characteristics of being relatively good in anti-separation properties, tensile resistance, anti-cracking properties, self-filling properties, gap through properties, size stability and the like.