Abstract: A computer casing with high heat dissipation efficiency comprises a lateral plate at an outer side of the supporting seat; a fan installed on the lateral plate; a supporting seat installed at an inner side of the lateral plate; a mother board installed to have a predetermined space to the supporting seat; a processing unit of a computer on the mother board; and a flow guide plate installed between the lateral plate and the flow guide plate; the flow guide plate being formed with a plurality of through holes at positions corresponding to those of the fan for sucking air to the fan; the flow guide plate having a plurality of ribs at an outer side thereof; the ribs being formed as flow channels for guiding air in the computer casing to the fan. The flow guide plate has a plurality of via holes which are arranged randomly on the flow guide plate; and edges of the flow guide plate have a plurality of edge holes.