A host unit case of a computer capable of being set up easily with detachable plate-shaped components includes an upper cover, a lower cover, a front wall, a rear wall, a main board support wall, a first support frame, a second support frame, a connecting plate, a third support frame, a left side plate, a right side plate and a panel. The host unit case is easy to be disassembled as pieces of plates for the smallest volume can be reached at the time of being packaged such that space occupied by the stacked components can be reduced tremendously for saving storage space and lower delivery cost.