Abstract: In this study, the interface failure under the joint action of constant compression and periodical anti-plane shear is investigated. With the so-called "shear beam model", analytical solutions are developed for the evolution law and the distributions of shear stress and displacement along the entire length of the interface during unloading processes. Results indicate that, owing to the existing of the damage process zone ahead of the crack tip, unloading is inelastic and accompanied by friction and damage dissipation. Furthermore, "stress locking" occurs if unloading process does not cover the damage zone left by loading process. Consequently, "shocking load" may occur in ensuing reloading process.