In order to grasp the influence of the dry-wet circulation on rock mechanics characteristics, taking the sandstone as an example, a series of shear tests were conducted by YZW50 microcomputer control electric stress direct shear apparatus, 6 kinds of tests of different dry-wet circulation number were set, which respectively were 1, 5, 10, 15, 20 and 30 times. The test results show that the shear characteristics of sandstone have obvious wetting-drying effect, when the dry-wet number is 30 times, the cohesion is 7.31MPa, the internal friction angle is 34.82°, and comparing with 1 times, native state, the falling range of which are severally up to 37.31% and 20.59. In addition, with the increase of dry-wet number, the failure characteristics of sandstone are also changed, and a transformation law from brittleness to ductility is showed.