Composite pylons with an I shape applied for 110 kV transmission lines have the advantages of being lightweight, less width of the corridor, and construction and maintenance friendly. However, research on the electric field distribution and lightning protection characteristics of this composite is currently lacking. In this paper, a 2D axisymmetric model of the pylon is developed to analyze the electric field distribution using the finite element method (FEM). The electric field distribution along the surface of the cross-arm and around the clamps is presented. After configuration optimization, the electric field distribution of the clamps and sheds is adjusted to meet the design criteria. The lightning transient overvoltage and critical current of the pylon are analyzed using an electromagnetic transient model, based on the optimized pylon configuration. The results indicate that an I-shaped composite pylon has a smaller shadow area and a lower backflash rate compared to steel towers of the same voltage level. This research provides valuable references and lays the groundwork for composite pylon design.