The invention relates to a method for manufacturing a barb groove of a plant fiber molding bowl cover. In the method, an external die which is matched with the lateral outline of the molding bowl cover is covered outside the plant fiber molding bowl cover subjected to hot-press reshaping; a traverse annular chute is formed at the position corresponding to the barb groove preformed on the bowl cover on the external die to accommodate a group of sliding blocks for forming, and a convex forming strip is arranged on the inner edge of each sliding block; an internal die is accommodated in the molding bowl cover, an ejector block is accommodated in the middle of the molding bowl cover, and the internal die and the ejector block are matched with the outline of the molding bowl cover; an annular concave bearing groove is formed at the position corresponding to the barb groove preformed on the bowl cover on the internal die, and the position and outline of the annular concave bearing groove are correspondingly matched with those of the forming strips; during manufacturing, the external die, the internal die and the ejector block are closed, the sliding blocks move inwards, so that the forming strips of the sliding blocks are pressed against the surface of the molding bowl cover, and the sliding blocks continue to move, so that the surface of the molding bowl cover retracts to the bearing groove of the internal die with the outline deformation of the forming strips to form an annular barb groove.