The standpoint(hypothesis) that the orientation of shear strength of rock structure face was proved by simulation tests.In the tests it was found that the shear strength is different when shearing a rock along a joint with asymmetrical profiles in different orientation,the orientation of shear strength is relative to the percentage of upward steps(upward slop) to total steps in fractal curve of rock structure face,which was measured by yard-stick method and the most undulate degree of rock structure face.