Abstract: With the theory of stress wave, it discussed mechanism of jointed rock loosing under blasting load. And this was verified by a numerical simulation using the dynamic finite element method. Results show that, compression of blasting load can store strain energy in rocks and quick unloading of the stresses can lead to elastic recovery, which are the essential reason for rock loosing during blast excavation. Blast disturbance can induce rock loosing, typical characteristics are shear moving of rocks in the normal direction of excavation surface and opening of weak planes in the parallel direction. The dynamic finite element method, which adopts Lagrange coordinates, can be used to simulate better the loosing process of jointed rock under blasting load. For example, the program of ANSYS/LS-DYNA is good for this case.