The invention discloses an integrally formed packing box and a forming mould and method for forming the packing box. The packing box comprises a bottom plate, a left side plate, a left cover plate, a front side plate, a front cover plate, a right side plate, a right cover plate, a rear side plate and a top cover; the packing box is formed by a piece of paper though bending and fastening; the paper comprises a first folding sheet, a second folding sheet, a fourth folding sheet, a fourth folding sheet and a fifth folding sheet, which are integrally connected; an insertion tongue is arranged at the free end of the fourth folding sheet and a socket which is matched with the insertion tongue is arranged on the second folding sheet; the first folding sheet is bent to form the left side plate and the left cover plate; the second folding sheet is bent to form the front side plate and the front cover plate; the third folding sheet is bent to form the right side plate and the right cover plate; the fourth folding sheet is bent to form the rear side plate and the top cover; the left side plate, the front side plate, the right side plate and the rear side plate are connected to form the bottom plate; and the fifth folding sheet is bent to be clamped between the bottom plate and the top cover. The whole packing box is simple in structure, convenient to process, safe, environment-friendly and low in cost.