Abstract: The microstructure of soil has a great influence on the macroscopic mechanical properties. Therefore, to study the relationship between the macroscopic mechanical properties and the microstructure evolution of soil under the cyclic loading, a miniature dynamic triaxial apparatus is developed, which is suitable for industrial micro CT (computerized tomography) scanning. The apparatus is mainly composed of the acquisition control system, loading device system, and air-liquid converter. It has the advantages of small volume, miniaturization of the specimen (diameter × height=10 mm×20 mm), convenient to operate, strong compatibility, and the specimen can be rotating-scanned without refitting the existing CT equipment. By using the miniature dynamic triaxial apparatus and conventional dynamic triaxial apparatus, a series of unconsolidated-undrained triaxial tests on Toyoura sand under cyclic loading and different confining pressures (50, 100, 200 and 300 kPa) are carried out, and the initial dynamic elastic modulus (E₀), dynamic shear modulus (G_d) and damping ratio ($\lambda$) are comparatively analyzed. The results show that the experimental curves of the initial dynamic elastic modulus (E₀), dynamic shear modulus (G_d) and damping ratio ($\lambda$) exhibit a similar evolution. The difference of experimental data is small, thus, the reliability of the miniature dynamic triaxial apparatus is verified.