A fan control device receives a target revolution signal to control a rotation speed of a fan. The device includes a temperature measuring module, a revolution modulating module and a driving module. The temperature measuring module generates a temperature value according to an ambient temperature of the fan. The revolution modulating module is electrically connected with the temperature measuring module, receives the temperature value, and generates a control signal according to the temperature value and the target revolution signal. The driving module is electrically connected with the revolution modulating module, and generates a driving signal to drive the fan according to the control signal. In addition, a fan control method, which is applied to the fan control device, is also provided.