Simulated rock joint samples with second-order asperity are made of artificial material. A series of constant normal load (CNL) cyclic shear tests are carried out to study the deterioration law of shear mechanical characteristics during process of cyclic shearing. Based on the experimental results，it can be found that the second-order asperity has an important influence on the shear mechanical properties of joint samples under cyclic shear loading. The shear strength

shear stiffness and dilatancy angle decrease with an increase of shear cycles

and decay more quickly with an increase of second-order asperity height. The influence of second-order asperity on the shear mechanical properties is mainly reflected in the first shear cycle with higher height of second-order asperity under higher level of normal stress

and it has no obvious effect on subsequent shear cycles. On the other hand

the influence is reflected more clearly during the begging of the shear cycles to the joints with smaller height of second-order asperity under lower level of normal stress. Finally

based on the theory of Hertz contact mechanics

a spherical contact microscopic model of asperity on the joint surface is proposed; and the mechanisms of macroscopic phenomenon during cyclic shear tests are revealed by the model.