This study presents a comprehensive experimental assessment of three hybrid mooring systems for a heaving-buoy wave energy converter. Free decay model tests are conducted to study the natural periods in heave, pitch and surge modes of the buoy when it is moored with different mooring configurations. A series of regular and irregular wave model tests are carried out to investigate the hydrodynamic responses of the point absorber as well as mooring dynamics. The effects of wave period, incident wave height and mooring configuration are evaluated. Besides, the influence of mooring configuration on buoy motion is discussed. To study the short term extreme dynamic tension, the traditional Weibull distribution, Weibull distribution based on tail data and peaks-over-threshold method are applied. The results showed that the Weibull distribution failed to present accurate extreme dynamic tension prediction when the snap events occur frequently, while the other two methods showed good performance despite of number of snap events. Based on the results of energy production performance and extreme dynamic tension, a novel mooring line design is suggested, which helps to reduce mooring dynamic tension.