The utility model relates to a compound cross arm, it includes that insulator and cladding are in insulator outlying full skirt, the full skirt includes that the cladding is in insulator's sheath portion and by a plurality of umbrella pieces that sheath portion outwards extends, sheath portion includes the edge district and a plurality of district of trampling are trampled to a plurality of non -s that the axial of insulator set up in turn, be located the umbrella piece top of trampling the district has been seted up and has been exposed the breach of sheath portion, it forms rather than the breach that corresponds and to supply the hole of trampling of trampling to trample the district. The hole is trampled through the setting to above -mentioned compound cross arm to can make the staff the installation trample when examining and repairing trampling the hole in, and then can walk on compound cross arm. The utility model also provides a transmission tower.