The utility model discloses an insulator crossarm, including main part, strengthening rib and insulating the pad, the main part is hollow rectangle tube, and the top surface and the bottom surface of main part are equipped with insulating the pad respectively, and the fixed insulating mounting hole that fills up is all opened to the top surface and the bottom surface of main part, and it has the T connected in star to open on the opposite face of the inside left and right sides of main part wall, the axial setting of main part is followed to the T connected in star, the strengthening rib is fixed in the T connected in star. The utility model has the advantages that: the terminal surface is equipped with insulating the pad about the main part, and insulating pad has not only increased the insulating nature between main part and the insulated terminals, protects the main part surface not by the scratch moreover, it has the T connected in star to open on the opposite face of the inside left and right sides of main part wall, is equipped with the strengthening rib in the T connected in star, very big increase the mechanical properties of main part, increased the anti bending strength of main part.