This study aims to develop an oscillatory wave-energy acquisition system with adjustable system characteristics. The system is designed to efficiently acquire energy from the sea waves with a wide frequency band. Based on the past studies, the oscillatory wave-energy acquisition system, designed previously, can only acquire energy from the sea waves with a narrow frequency band. Such a limit causes the system to have a low efficiency in acquiring power if the wave has a large frequency band. The main goal of this novel design to allow the system adjusting its system characteristics, based on the dynamic characteristics of sea wave, to attain the optimal power acquisition. In the study, different types of oscillatory systems are first examined whether they are effective to transform their dynamic characteristics when the system parameters are varied. The effectiveness of such transformation is evaluated through an optimization procedure. This procedure is to evaluate whether the frequency response of system can acquire the highest power from a given property of sea wave. Through a detailed analysis, the system structure of a three degree-of-freedom oscillatory wave-energy system is chosen for current purpose. A careful study about the effectiveness of dynamic transformation, via the adjustment of different system parameters, is then studied. The study shows that the selected system with adjustable capability can effectively acquire energy from a sea wave with large frequency band. The acquired efficiency can increase up to 70% compared to the earlier system.