In order to solve the high energy consumption problem of fittings with steel or aluminum alloy and reduce the line loss, dozens kinds of engineering plastics were studied and the PA66 nylon composite had been determined as the basic material. Then, some modified composites like glass fiber, flexibilizer, ozone resistance and corrosion resistance were mixed in the basic material. After repeated counts of tests and formulation optimization, a new kind of composite material was successfully developed, with the tensile strength of 210 MPa and the elongation of 4,5%, which had some good performances just as small specific gravity, good insulation, resistance to radiation, energy conservation, environmental protection, antifatigue, etc. The spacer and suspended clamp based on this modified composites were designed, trial-produced and tested, whose results showed that they could meet the requirement of national standard and electric power industry standard. The suspension clamps with the modified composites have been well applied in 35 kV and 220 kV overhead transmission lines.