Abstract: In order to ensure the safe and reliable operation of the carbon fiber composite core conductor after the line capacity expansion, the high voltage end core rod end temperature of the composite insulator corresponding to the conductor temperature is calculated theoretically. Then the thermal insulation effect of adding one piece of porcelain insulator between the suspension composite insulator and the conductor is tested by experiments, and the temperature rise of the metal ball socket of the superimposed porcelain insulator and the exposure temperature of the metal ball socket under the Sun are added. It is found that adding 1 piece of porcelain insulator can not ensure the mechanical properties of composite insulator mandrel, so porcelain (glass) insulator string should be used.