Based on the traditional configuration of the off-grid wind generation system with battery energy storage, this paper provides an energy control method and a complete system sizing scheme, mainly including wind turbine generator and battery, to achieve continuous operation without an excess energy consuming device and decrease the system size and cost. In this paper, Hong Kong and Denmark are selected to do the case studies, in where system sizes are designed using the proposed scheme. Simulation results show that, based on continuous operation as the precondition, the designed sizes of wind turbine generator and battery are the required minimum ones, which can make both Hong Kong and Denmark achieve yearly energy balance between supply and demand. Therefore, simulation results show the validity and rationality of this system sizing scheme.