As an important part of distribution network, distribution transformer(DT)has low insulation level and is vulnerable to lightning overvoltage. The safe operation of distribution transformer is very important to the stability and reliability of distribution network. In this paper, the scattering parameter measurement method is used to establish distribution transformer model, amplitude frequency characteristics is obtained by impedance measurement and data processing of distribution transformer circuit fitting and particle swarm optimization algorithm based on simulated annealing is intriduced to optimize the model. The measured results show that the measurement results of the distribution transformer under lightning stroke are in good agreement with the simulation results established in this paper. Based on the broadband model, the influence of shock corona on voltage distribution of distribution transformer and the lightning protection measures of distribution transformer are analyzed.The results show that the shock corona significantly reduces the amplitude of the transformer over voltage,and the lightning protection effect of lightning arrester installed on the low voltage side of the transformer substation is obvious.