The utility model discloses a knife sharpener which comprises a knife sharpening base structure and a folding handle structure installed on the knife sharpening base structure. The knife grinding seatstructure comprises a knife grinding bottom plate, a knife grinding seat covering the knife grinding bottom plate and a knife grinding structure mounted on the knife grinding seat, a circular grooveis formed in the knife grinding seat, a limiting cylinder extends upwards from the interior of the groove, and a fixing column extends upwards from the knife grinding bottom plate; the folding handlestructure comprises a handle bottom plate and a handle cover body fixed on the handle bottom plate; the handle bottom plate is downwards provided with a circular convex seat embedded in the groove; the folding handle structure further comprises a locking column arranged on the fixing column in a sleeving mode, a locking button installed at the upper end of the locking column, and a reset spring arranged outside the fixing column in a sleeving mode and clamped between the locking column and the bottom plate. The side face of the locking column extends outwards to form a locking block, a first locking groove capable of being clamped with the upper end of the locking block is formed in the inner side wall of the protruding base, and a second locking groove capable of being clamped with the lower end of the locking block is formed in the inner side wall of the groove.