A control method for a wind power generating system includes the following procedures. When a rotational speed control condition is satisfied, a wind turbine is switched to operate under a rotational speed control mode to limit the electricity power by a maximum power point shifting manner. When a speed of an external wind is greater than a predetermined wind speed, the wind turbine is switched to operate under a safety mode to decrease a rotational speed of the wind turbine by a maximum torque extraction manner to protect the wind power generating system. A wind power generating system is also disclosed herein.