Abstract: In order to quantitatively describe the lightning channel characteristics of 3D channel intracloud (IC) lightning, we establish the relationship between the lightning radiation sources and the radar echo at the synchronization time, and provide a useful reference for lightning early warning. Based on the data from the 3D low-frequency magnetic lightning mapping array in Nanjing, three typical ICs in a severe convective weather system are observed and studied. The main results are as following: the initial processes of the three ICs are almost vertical upward from about 6 km to the height of about 10 km and then approximately develop horizontally; the average propagation speed is about 2.9×10⁵−3.6×10⁵ m/s; there are two ICs that discharge in two different heights range with different propagation direction, and the other one is in the same height range with the same propagation direction; the lightning radiation sources are basically concentrated in the strong radar echo above 30 dBZ. Time difference of arrival (TDOA) method via cross-correlation technology are used to spatially locate the radiation source of the ICs, which can map the 3D channel structure of the flash, especially the characteristics of the initial stage in real time, and the quantitative mapping relationship between the radiation sources and the radar echo in the initial stage of the ICs in Nanjing area is also obtained.