Influenced by the Northeast China cold vortex and warm and moist airflow in the northwestern part of the subtropical high, a damaging squall line with cell merging process took place in Beijing area on 27 July 2015. Based on data from Beijing Lightning Network (BLNet), S-band Doppler radar observations, and radiosonde data, the characteristics of total lightning activity associated with this severe squall line are analyzed. The results show that the lightning activities generated by the squall line were mainly IC (intra-cloud) lightning flashes; CG (cloud-to-ground flashes) were dominated by NCG (negative CG); in the dissipation stage, the ratio of PCG/CG (positive CG to CG) increased sharply. About 93% of total lightning flashes were distributed within 10 km distance of the convection line, while flashes occurring in the stratiform region were relatively fewer. PCG was more likely to occur in the transition zone and stratiform region; the occurrence of lightning in the stratiform region might result from the advection of charged particles from convective region through transition zone. There existed a large amount of water vapor concentration during the convection merging, and the peak of lightning lagged 24 minutes behind the peak of vertically integrated liquid water content (VIL). The Variational Doppler Radar Analysis System (VDRAS) is used to retrieve the three-dimensional wind field during the squall line process, and the reasons for the increase in lightning during the merging process are studied. According to the wind field retrieved from the VDRAS, the merging of convective clouds mainly occurred in the lower convergence zone; after the convection merging, the extent and intensity of the updraft both became intense, and the lightning activity became more active. Lightning was mainly concentrated in the region with strong vertical wind shear, while a small fraction of flashes occurred in the rear of the convection zone where downdrafts were observed to appear.