The disposal of high-level radioactive waste is one of the important factors restricting the development of nuclear energy. At present, China has determined the Tamusu area of Inner Mongolia as a pre-selected area of clay rock type repository. The difficulty of original rock mining and the high cost of acquisition have seriously affected the scholars’ research on the properties of Tamusu clay rock. Artificial samples simulating the lithofacies characteristics of Tamusu clay rock were prepared by similarity principle. Through testing, an optimal ratio group was selected that aligns closely with the properties of the Tamusu clay rocks, fulfilling the laboratory’s sample requirements. The influence of each component in the ratio on the mechanical properties of similar samples of clay rock, such as uniaxial compressive strength, tensile strength, Poisson’s ratio, elastic modulus, internal friction angle and cohesion, was analyzed by mechanical test. Through experiments, the optimal ratio group with the closest properties to the original rock of Tamusu clay rock was successfully screened out. The permeability and diffusion test experiment was carried out on the optimal group of samples. The measurement results show that the permeability and diffusion coefficient are in the same order of magnitude as the original rock data.