A rack server system is provided. The rack server system includes a plurality of server modules, a plurality of fan modules, a rack management network and a rack management module. Each of the server modules comprises a baseboard management controller (BMC) to monitor and manage a work status of the corresponding server module. Each of the fan modules includes a plurality of fans. The rack management network is connected to the BMC of each server module. The rack management module receives the work status from the BMC of each server module through the rack management network to control and manage the server modules and to control speed of the fan modules.