Abstract: Based on the data obtained from the 2015 summer campaign in Beijing area, including the total lightning location data from Beijing Lightning Network (BLNET), S-band Doppler radar data, ground-based automatic weather stations observations and radiosonde data, the evolution of lightning activities during a severe squall line process that occurred over Beijing metropolitan region on 7 August 2015 was analyzed. Its relation to convection region and surface thermodynamic condition was also discussed. According to radar echoes and lightning occurrence frequency, the whole squall line process can be divided into three stages (developing, intensifying and weakening), and the intra-cloud (IC) lightning flashes predominated during all the three stages in general. In the developing stage, several isolated γ mesoscale convective cells rapidly developed. With the echo top of the storm cell over Beijing metropolitan region extending to -20℃ level, lightning activities significantly increased, and the lightning radiation sources gradually spread to upper altitudes, but lightning rate was still less than 80 flashes/min for the whole system. In the intensifying stage, the flash rate increased rapidly, which was associated with the merging process of the cells. When the squall line formed, the volume of strong radar echoes (＞40 dBZ) increased significantly for both above and below 0℃ levels, and the total flash and cloud-to-ground (CG) flash peaked with rates of 248 flashes/min and 18 flashes/min, respectively. Negative CG flashes accounted for 90% of the total CG flashes. The lightning radiation sources were mainly detected in the linear convection area, and the number of radiation sources peaked within the layer of 5-9 km. In the weakening stage, the core of the squall line dropped below 0℃ level and quickly decayed, with the radiation sources obviously sloping backward to the area of stratiform clouds. About 95% of total flashes occurred within 10 km of the convective line, namely the convection and transition region. During intensifying and weakening stages, radiation sources reached active period simultaneously in the convection and stratiform region, while during the weakening stage, radiation sources in the convection region declined abruptly in the number. Lightning flashes mainly occurred over regions with strong surface equivalent potential temperature gradient induced by the outflow of convective cold pool and the relatively warm moist airmass from the plain.