Abstract: It is of great significance to further clarify the relationship between thunderstorm dynamics, microphysics and lightning scale. In order to fully understand the influence of the microphysical process of the thunderstorm cloud on the lightning scale, a thunderstorm process was simulated by using the three-dimensional thunderstorm cloud initiation and discharge model, and the correlation analysis was conducted between the content of each hydrogenic particle in the thunderstorm cloud and the scale of the cloud flash channel. Two typical intra-cloud lightning cases were selected to analyze the distribution of ice crystals and graupel particles during the occurrence of the two intra-cloud lightning events, as well as the differences between their electric generation rate, spatial charge structure distribution and lightning channel scale. The results show that graupel particle content has a significant positive correlation with intra-cloud lightning scale, while the microphysical characteristics of other hydrogenic particles have no significant correlation with intra-cloud lightning scale. The larger the size of graupel particles is, the faster the falling speed is. The non-induced electric generation process of graupel particles colliding with ice crystals and the induced electric generation process between graupel particles and cloud droplets contribute to the space charge structure of thunderstorms. Graupel particle content has a significant influence on the development of cloud flash pilot channel by changing the content and distribution range of space charge pile.