Abstract: Total lightning data observed by the SAFIR3000 3-D lightning locating system were combined to the data of radar to analyze the characteristics of the lightning activities and electric structures of a hailstorm occurring in Beijing on 31 May 2005. The results indicated that there were two active periods for lightning activities during the hailstorm process. The hail shooting was found in the first period. After the end of the hail shooting, lightning frequency was decreased suddenly. However, more lightning activities occurred in the second period with lots of them appearing in the cloud anvil region. The peak time of lightning activities was prior to the hail shooting about 5 minutes. Only 6.16% of the total lightning discharges were cloud to ground (CG) lightning discharges. Among them, 20% were positive cloud to ground (PCG) lightning discharges. In addition, the PCG lightning discharges before the hail shooting were more than those after the hail shooting. In the stage of the hail shooting, the electric structure of the hailstorm was inverted, i.e., the main negative charge region lay around the -40 ℃ level, and the main positive charge region lay around the -15 ℃-level. In addition, a weak negative charge region had existed below the positive charge region transitorily. With fast and persistent adjustment after the hail shooting, the electric structure changed to a pattern of usual tripole with the upper positive charge, the middle negative charge and the lower positive charge configurated. However， the electric structure was tilted under the action of the west wind in the middle and upper levels. It was found that lightning activities and electric structures showed a close relationship with dynamic and microphysical processes in the hailstorm. The reason why the inverted electric structure formed was discussed in the article. It was believed that it was easier for severe storms with very strong updraft to form inverse tripolar electric structure than for usual storms and produce more PCG lightning under the effect of the lower two charge regions.