A blade server includes a casing, a plurality of blade modules, and a function module. The casing has a first end and a second end being opposite to each other. The blade modules are configured on the first end of the casing, and may be moved in or moved out from the first end of the casing. Each blade module includes a first tray, a main board module, and a plurality of hard disk modules. The main board module is configured on the first tray. The hard disk modules are detachably disposed on the first tray, and are electrically connected to the main board module. The function module is configured on the second end of the casing, and may be moved in or moved out from the second end of the casing.