In order to solve the problems of limited wind power utilization range and inefficient charging and discharging control of the storage battery for small off-grid wind power generation system，a vertical-axis off-grid asynchronous generator wind power system is developed.The asynchronous generator can run in a wider speed range and self-start.By use of flexible control strategy，the active and reactive power output are regulated together to realize bi-directional flow of the energy and coordination control between wind turbine and the storage battery.The slip-frequency control strategy is employed in the induction generator to regulate the pulse width modulation（PWM）converter to control the output power when the wind speed and load change.The charging and discharging of the storage battery is controlled by a grading current-limit strategy with a power unloading device connected with the DC bus.All these strategies ensure the balanced and stable operation of the proposed system.Experimental research on a5.5kW prototype system is carried out，and the results verify the feasibility of the system design and control strategy.