A fan system includes a control device and a fan device. The control device has a first node, a rotation speed signal generation circuit and a rotation speed reading circuit. The fan device has a second node, a signal transforming circuit, a motor driving circuit, a motor and a fan. The first node is electrically connected with the second node to set up a transmission route between the control device and the fan device. The rotation speed control signal and the motor rotation speed signal are transmitted via the two-way transmission route, and the control device controls the fan device via a wired or wireless transmission route. A motor control device is also disclosed.