Heaving buoys are common devices for wave energy conversion. In recent years, many researchers have been devoted to improve their energy-absorbing capability by configuration optimization. Traditionally, the operation of wave energy converter (WEC) has to be interrupted for safety when waves become excessively strong. In this paper, in order to render the WEC able to work under a wide range of wave conditions so as to enhance the energy-harvesting capability and increase the total operation hours and total power production, a new type of buoy, controllable-valve buoy (CVB) is proposed. It is a hemisphere-cylinder combined buoy with a hollow channel covered by a controllable valve that can operate in two modes. In gentle sea states the valve is closed and the buoy absorbs wave energy to a large extent, while in rough sea states the valve is opened and the buoy is able to work and produce an acceptable power. The geometrical parameters of CVB are optimized via a systematic method combined with wave statistics of the target installation site. The radius and the draft of the optimized buoy are 4.8 m and 8 m, and it has a hollow channel with a radius of 2 m. Simulation results show that the optimized buoy demonstrates a good performance in both closed and opened mode.