Since wind power is more versatile and unpredictable than traditional thermal power, increasing wind penetration level generally needs more spinning reserve, which is not economical. Frequency related voltage control can be helpful to solve this problem. When frequency becomes lower due to a sudden sharp decrease of wind farm output, load voltage can be lowered to decrease the demand of active power and improve the grid frequency after the accident. And then AGC is adopted to restore frequency to normal level. Given the loss of load probability (LOLP) or loss of load expected (LOLE), the quantity of spinning reserve can be obtained by probability calculation. This method can also be used when large generation (like 1000 kV UHV line) is lost to avoid load shedding. Simulation also validates the effectiveness of this method.