Due to China’s swift advancements in power grid technology and ongoing enhancements in the ecological environment, birds pose a great threat to the stable operation of overhead lines. To minimize the likelihood of bird excrement causing flashovers on overhead power lines, this paper takes the insulation drainage line as the object, and uses the finite element simulation calculation to study and analyze the insulation layer thickness (sheath thickness), bird droppings position, and semiconductor layer thickness. The impact of flashover properties on insulation drain lines. The results show that when the drainage line is coated with an insulating sheath, the electric field distribution close to the lower part of bird droppings can be enhanced; When the spacing between bird droppings and the grading ring or drainage line is reduced, the electric field strength at the base of bird droppings, grading ring, and drainage line surface rises with decreased spacing. Enlarging the insulating layer thickness can lower drainage line surface field intensity; as the thickness of the semiconductor layer of the insulation-covered lead wires increases, the surface field strength of the drainage line gradually diminishes.