Using the data from SAFIR3000 lightning detection network and Doppler weather radar, the characteristics of lightning activity in a squall line on July 31, 2007 were analyzed. In this study, the lightning activity and inferred charge structure of squall line were obtained. Our results reveal that: 1) the horizontal projection of the lightning radiation sources mainly corresponded to the high radar reflectivity area of the squall line, and 2) the vertical distribution of the lightning radiation sources developed from two layers into three layers. At the developing stage of squall line, the upper lightning radiation sources were centered at 11km MSL, while the lower radiation sources were located at 4km MSL. Assuming that the maximum lightning radiation sources were corresponding to the positive charge region, the squall line showed a dipole charge structure with an upper positive charge region and a lower negative charge region. At its mature stage, the entire squall line was characterized by a multi-layer charge structure with three layers of positive charge at 5km MSL, 9.5km MSL, and 13km MSL, and a two-layer negative charge region at 7km MSL and 11km MSL. •Lightning radiation source distribution of squall line was shown.•Inferred charge structure of a squall line was indicated.•We investigated the relationship of lightning activity and radar reflectivity.