The invention discloses a light foam sandwich composite material insulating rod. The insulating rod comprises an insulation cylinder and sandwich rods filled in the insulation cylinder. The insulating rod is characterized in that the insulation cylinder is made of epoxy resin based composite materials; the sandwich rods are made of light foam materials; the inner wall of the insulation cylinder and the outer walls of the sandwich rods are tightly fit; and the epoxy resin materials forming the insulation cylinder matrix are filled in the pores of the outer walls of the sandwich rods. The invention also provides three preparation methods of the insulating rod. The first preparation method comprises the steps of firstly forming a light foam sandwich rod, then winding reinforcing materials and impregnating the obtained product in epoxy resin glue solution. The second preparation method comprises the steps of firstly forming a light foam sandwich rod, directly winding pre-impregnated reinforcing materials and then curing the obtained product to obtain the product. The third preparation method comprises the steps of forming a hollow light foam sandwich cylinder, then winding reinforcingmaterials and spraying epoxy resin glue solution on the reinforcing materials, curing the obtained product and then foaming and filling the hollow parts to obtain the product. The insulating rod has the advantages of simple preparation process, light finished product mass, high bending resistance, good mechanical property, low cost, no hidden danger of interface breakdown and the like.