In the process of manufacture, operation and maintenance of transformer, metal particles will inevitably be introduced into its internal insulation oil. In order to explore the influence of metal particles on the insulation performance of oil-paper, this paper builds a test platform for debugging lightning impulse discharge of oil-paper insulation, and carries out experimental research on the influence of metal particles on the development characteristics of oil-paper insulation. In this paper, the difference of initial voltage and development process of streamer with different concentrations of metal particles is studied and verified by COMSOL simulation platform. The results show that metal particles can promote the beginning and development of the streamer. The length and speed of stop and development of streamer are positively correlated with particle concentration, while the starting voltage and breakdown voltage of insulating oil streamer are negatively correlated with particle concentration. The analysis shows that the interaction between metal particles in oil and streamer is the main reason to reduce the starting voltage of streamer, accelerate the development of streamer, and then reduce the breakdown voltage of insulating oil.