Abstract: The unloading fracture zone of high rock slope is very significant in rock slope engineering. In this paper, firstly, the basic regularities of secondary stress distribution resulted from slope excavation and river during cutting are studied, and then a general model for formation mechanism of unloading fracture zone is suggested. It reveals that the unloading fracture can be discriminated into two basic types, i. e. tensile fracturing and shear relaxing. Moreover, the engineering behaviors of the unloading fracture zone and its mechanical significance are discussed. On this basis, we propose a numerical simulation approach to the unloading fracture zone in slope excavation. Finally, as a typical example, the distribution of unloading fracture zone of high slope at Three-Gorges shiplock is figured out and its progressive development process is simulated numerically.