A packing box contains: an accommodation casing, a first side casing, a second side casing, multiple bottom casings of various sizes, multiple top casings of various sizes, and a plurality of binding straps. The accommodation casing includes multiple first and second spaced holes, the first side casing includes multiple first and second spaced orifices, and the second side casing includes multiple first and second spaced apertures. Each bottom casing covers a bottom of each of the accommodation casing, the first side casing, and the second side casing, and each top casing covers a top of each of the accommodation casing, the first side casing, and the second side casing. Each binding strap includes a fastener, a male fastening face, and a female fastening face, wherein the fastener fastens with the male fastening face and the female fastening face so that said each binding strap fixes the packing box.