Abstract: Lightning is a kind of long distance discharge phenomenon, and it often causes a variety of disasters which become more serious by the extensive use of electronic devices particularly. With deep understanding on physical processes of lightning occurrence and development, lightning leader model is established based on observational facts to study development of lightning leader and its interaction with structures and provide reference for lightning protection. In order to study the interaction of lightning leaders and structures, the connection process of leaders is simulated. A 2 dimension model of lightning leader is developed by simulating ambient potential distribution using an over relaxation method. In the model, the direction of next leader step depends on the position of a maximum potential gradient. Attractive radius in the model is defined by horizontal distance between initial axis of downward leader and connection point (such as lightning rod, the corner of building). The distance of final jump is defined by the distance between the tip of downward leader before final jump and connection point. Simulation results show that the length of stepped leader ranges from 13.8 m to 51.5 m. The induced charge of downward leader is about 0.03×10^-4-1.2×10^-4 C/m. The length of stepped leader and the induced charge of downward leader increase with the propagation of downward leader. These simulated results are consistent with the observation. Before the final jump, the turning of downward leader is not obvious. In the final jump, downward leader turns some direction towards the upward leader initiated from lightning rod. Simulation results are accordant with the previous simulation results. The interaction and connection process between downward leader and a structure with a width of 40 meters are simulated using this model. The corner of structure has some attractive radius and can compete with lightning rod on structure. In the design of lightning protection, attractive effect of corner to lightning leader can't be neglected. The design of lightning protection based on attractive radius of lightning rod under perfect conditions (such as isolated tip on the ground) is problematic and risky.