In this paper, the authors have investigated into the development of a new system of generating and controlling impulsive water pressure, that can be used for simulated model tests on the strength of structural components of ships subjected to impulsive wave-load. This hydraulic loading system is of a new design based on a unique principle and with simple devices. It is composed of two hydraulic chambers A and B, both of which are filled by water with nitrogen gas in A-chamber only and are separated by a test specimen such as a stiffened plate model of side shell plating of ships. Since the water pressure in both chambers is, in the initial stage, kept at the same level as of the prescribed peak value of the impulsive wave-load, the test specimen is balanced as being free of load. Subsequently, the water in B-chamber is forced to be quickly discharged through a rupture disc located at an end of the chamber, the pressure being dropped down to atmospheric pressure in some milli-seconds, while the pressure in A-chamber remains almost at the initial value by the effect of the accumulator thus causing an impulsive water pressure “gifle” acting on the test specimen. Then another rupture disc attached to A-chamber is broken by means of a shot-gun, and the water pressure is decreased to a certain level, corresponding to “bourrage” as usually observed in the patterns of impulsive wave-load. Performance test is first made on a small scale preliminary testing device, and then a pilot testing apparatus for 1 meter × 1 meter plate specimens is manufactured and examined on the characteristics of the water pressure vs. time relations of the system, which primarilly depend on the size of the chambers, diameter of the rupture discs and the rigidity of the test specimens, etc. Theoretical study is also made on the mechanism of generating the impulsive water pressure in this system by analizing the motion of water, the chambers and the test specimen, by taking into account of compressibility and damping of water as well as elastic and plastic deformations of the specimens. The results of the analysis have indicated a similar tendency in the pressure vs. time characteristics of the system to those obtained by the experimental results on the pilot testing apparatus. Thus, it is concluded that the impulsive wave-load simulating system of this type can be used for the structural model tests under load condition of a controlled pressure pattern similar to those experienced on actual ships.