Abstract: Sources of charge structure for the individual strokes of four multiple-stroke flashes to ground have been estimated by using measurements of the electrostatic field changes obtained at 5 sites on the ground beneath thunderstorm. The result shown that the altitude of neutralized negative charge is between 2.74～5.41 km above the ground (the corresponding ambient temperature is -2.0～-15.0℃), while that of neutralized positive charge is less than 2.0 km above the ground (the corresponding ambient temperature is +5℃). The charge neutralized by positive discharge is about 7 times larger than that neutralized by negative discharges. Positive and negative flashes usually follow cloud discharges which lasted 170～300 ms and occurred between lower positive charge region and main negative charge region during the developing stage and early active stage of thunderstorm. The comparison with radar echo has shown that the negative discharge initiates in the regiom greater than 20 dBz or near the edge of the region with severe echoes greater than 40 dBz, while positive discharge initiates in the weak echo region.