The complicated fracture structure of bed rock was introduced to study the process and mechanism of propagation of fluctuating pressure due to jet impingement downstream of high dams. Applying the Monte Carlo method, the transient model of fluctuating pressure propagation within an imitated rock fracture network was established. The transient time process of pressure fluctuation within each fissure and the special distribution of the intensity of pressure fluctuation were obtained by numerical simulation. It was concluded that the transient distribution of the fluctuating pressure of any node, with typically anisotropy, was the result of the propagating, reflecting and interating of pressure waves within fissure cells. The fluctuating intensity obeyed on the normal distribution. Through the spectrum analyzing, it was verified that the fluctuating pressure of any node not only lied on the pressure forced outside to the control volume, but also were determined by the geometric and physical characters of the fissure cells which are joined with the node or reached it through other cells.
