Server equipment having a fool-proof structure includes a casing and a tray. The casing includes a storage unit area, a plurality of motherboard areas, a back plate, insertion slots and a fool-proof device. The fool-proof device selectively has an engagement member at a first height or an engagement member at a second height. The tray includes a motherboard, a connection card and a protection housing. When the protection housing is in contact with the engagement member at the first height, the connection card is correspondingly inserted into the insertion slot. When the protection housing is in contact with the engagement member at the second height, the connection card is spaced from the insertion slot by a distance. Accordingly, the connection card is prevented from being inserted to a wrong insertion slot, so damage to the connection card is avoided.