Abstract: The absorption sphere shutdown system is the second shutdown system of 10 MW HTR. The absorption sphere contains 25% B₄C, dispersing in graphite matrix. The crushing load，which is an important performance parameter of the absorption sphere, closely relates to the diameter. The effect of graphite sphere diameter and density on the crushing load was studied using the graphite sphere to simulate HTR absorption spheres. Three kinds of graphites with different densities were chosen and processed into five types of spheres with different diameters, and then the crushing experiment was conducted. The results show that the crushing load of the sphere is proportional to the square of the diameter, and increases with the density. For a certain diameter of graphite sphere, increasing the density of the sphere is an effective way to enhance the crushing load.