The invention relates to the field of automobile engine cover manufacturing and aim at providing a flanging device and a flanging method for an engine cover. The flanging device for the engine cover comprises a rack of an upper plate in which two through holes are formed, two climbing mechanisms, a plurality of retaining mechanisms, at least two pre-bending mechanisms, a plurality of locating rods, a transfer delivery mechanism, a flanging preforming die and a flanging forming pressing die, wherein the two climbing mechanisms are located in the rack and respectively opposite to the through holes; five of the retaining mechanisms are respectively located at one end and two opposite outer sides of the first through hole, and the other retaining mechanisms are respectively located at one end and two opposite outer sides of the second through hole; the at least two pre-bending mechanisms are respectively located at the two opposite outer sides of the first through hole; the locating rods are respectively located at the outer side of one end of the first through hole and the outer side of one end of the second through hole, and are connected with the upper plate; the flanging preforming die is located above the first through hole; the flanging forming pressing die is located above the second through hole. The flanging device for the engine cover is stable in flanging quality and high in efficiency.