Abstract: The ultra-deep marine carbonate rock reservoirs are abundant in oil and gas resources and are an important field of increasing reservoir and increasing production in our country. Ultra-deep oil and gas reservoirs are affected by high stress and high temperature, and the mechanical properties of rocks change significantly at this time, which increases the difficulty of rock breaking, increases the probability of drilling accidents, and restricts the exploration process and benefit development of ultra-deep oil and gas resources. The mechanical test of ultra-deep marine carbonate reservoir rock under different confining pressure is carried out by combining triaxial compression test and industrial CT scanning reconstruction, and the microscopic fracture morphology of the test specimen is reconstructed. The results show that confining pressure has an important effect on the strength, deformation, and fracture characteristics of rock. The peak strength, elastic modulus, peak strain, and residual strength of rock increase with the increase of confining pressure. Under uniaxial conditions, the rock is dominated by axial fracturing, which gradually changes to shear failure with the increase of confining pressure. The fracture quantity, fracture volume, and average fracture width of rock under uniaxial compression are higher than those under triaxial compression, which indicates that confining pressure inhibits fracture propagation. The research results are of great significance to the exploration and development of deep oil and gas resources.