Abstract: In recent years, improvement on construction technology makes it possible to adopt a monolthic concrete slab as a new type of surface protection for an overtopped cofferdam. To demonstrate the feasibility of this technique, a study on the stability mechanism of the slab is needed, and particularly the oscillating pressure under the slab is a key factor in cofferdam stability. Using model tests, we have studied the distribution characteristics of the oscillating pressure and obtained the relationships of this distribution versus slab slope, discharge, and hydraulic jump location. The test results show that the signals of flow pulsation on the slab are characterized by low amplitude, broadband, and normally distribution.