The invention discloses a fan control method and system for a transformer substation. The method comprises the steps of obtaining the indoor temperature of the transformer substation; obtaining the outdoor temperature of the transformer substation; calculating the difference value between the indoor temperature and the outdoor temperature; judging whether the difference value is larger than a first preset threshold value or not, and obtaining a first judgment result; when the first judgment result shows that the difference value is larger than the first preset threshold value, turning on a fan inside the transformer substation; when the first judgment result shows that the difference value is not larger than the first preset threshold value, turning off the fan. By the adoption of the fan control method and system, the fan can be automatically controlled to be turned on or turned off according to the actual environmental conditions, so that the fan does not need to be continuously kept on, and noise produced by the fan is reduced.