The invention discloses a granary ventilation control system and a granary ventilation control method. The granary ventilation control system comprises a granary inside humiture sensor, a granary outside humidity sensor, and a controller. The granary inside humiture sensor is used to acquire the temperature and the humidity inside the granary. The granary outside humidity sensor is used to acquire the temperature and the humidity outside the granary. Under the control of the controller, when the difference between the temperature inside the granary and the temperature outside the granary is greater than the first preset threshold value, the ventilation can be carried out in the first way; when the difference between the temperature inside the granary and the temperature outside the granary is greater than the second preset threshold value, the ventilation can be carried out in the second way; and the first preset threshold value is smaller than the second preset threshold value. The ventilation of the granary and the ventilation way can be controlled according to the temperature and the humidity inside and outside the granary, and the automatic control of the granary ventilation can be realized, and therefore the power consumption can be reduced, the good ventilation effect can be achieved, and the energy-saving and emission-reduction effect can be realized.