Abstract: It is of great significance in theoretical analysis to investigate the non-coaxial behavior of the interface in tangential direction, which may emerge due to 3D loading. The test results in one-way circle shear path demonstrate that: (1) the non-coaxial angle gradually decreases from 90? in the first cycle, and then tends to be a stable value of about 45o with cycles; (2) the tangential displacement increment per stress first increases, subsequently decreases for small stress amplitude after shearing to some extent and then tends to be stable with cycles. As for the test in two-way circle shear path, it is found that: (1) the non-coaxial angle decreases from 90? in each cycle and tends to be stable value of about 45?, which varies little in different cycles but the symbol is opposite in neighboring cycles; (2) the tangential displacement increment per stress increases in a cycle and also tends to be stable, but the stable value decreases with shear cycles for small stress amplitude. It is also indicated that the shear stress amplitude has great influence on the non-coaxial behavior of the interface in tangential direction.