Abstract: For researching the triaxial mechanical properties and energy evolution laws of coal-rock assemblages under the action of supercritical CO₂, a supercritical CO₂ immersion system was used to perform immersion and triaxial compression experiments on 4 kinds of coal-rock assemblages with different height ratios. The experiments indicate that: (1) With the coal-rock height ratio augments, triaxial compressive strength and elastic modulus of the assemblage reduce, and the strain deformation gradually increase at the time of destruction. (2) After supercritical CO₂ immersion, the triaxial compressive strength and elastic modulus of the combined specimens decreased to different degrees; as the rise of the coal-rock height ratio, the reduction degree of the triaxial compressive strength and elastic modulus of the combined specimens increased. (3) After loading the damage of the assemblage, there are no obvious cracks in the rock part, and the damage mainly occurs in the coal body, while the destruction of the coal body after supercritical carbon dioxide immersion is even more fragmented. (4) The total energy, elastic energy and dissipation energy of the assemblage gradually decrease with the raise of coal-rock height ratio; supercritical CO₂ immersion reduced the total energy, elastic energy and dissipation energy of the assemblage, but the proportion of the dissipation energy augmented.