A heat dissipation device for a server is provided, composed of a fan body and a guide cover for concentrating airflows. The guide cover concentrates heat flows from a server computer and directs the heat flows to the fan body connected with the guide cover. The fan body includes a housing and at least a fan set, wherein the fan set is inserted into a passage formed by the housing, and a fan of the fan set operates to dissipate heat flows directed by the guide cover to outside of the server computer so as to enhance heat dissipation performances. Moreover, the fan set can he easily assembled or disassembled, and optionally replaced or altered in number thereof provided for the fan body, thereby attaining to flexibly in the use of the heat dissipation device.