The weak links in modern power grids will cause the expansion and development of accidents. The vulnerability assessment of the power grid and its components is of great significance for preventing large-scale power outages. This paper focuses on the vulnerability assessment of power grid lines, and establishes a comprehensive assessment system of line vulnerability that considers structural vulnerability, state vulnerability and environmental vulnerability. The environmental vulnerability part selects representative lightning strikes, icing, strong winds, pollution, wildfires and external damage as indicators of vulnerability. Then, based on the IEEE 39-bus system calculation, the result of the line vulnerability assessment is obtained, and compared with the calculation result of the existing method, the rationality of the constructed assessment method is verified. Finally, based on the evaluation results of the vulnerability of the line, the uniformity of the network structure is further analyzed. The results show that when a single index is used to analyze the vulnerability of the line, some vulnerable units will be omitted. The comprehensive index constructed by considering the structural characteristics, state characteristics and environmental characteristics can better evaluate the vulnerability of the line. The expansion and evolution of the network has the characteristic of "preferred connection", and high betweenness lines and nodes will inevitably form. By adopting "anti-optimal connection", for example, reducing the maximum value of the node degree can promote a more uniform network structure. This work is supported by the Science and Technology Project of the Headquarters of State Grid Corporation of China “Research on the Influence of Large-area Power Network on Buried Metal Pipeline Network Energy Safety Transmission and its Defense (No. 52170219001D).