In order to have a better understanding of the characteristics of lightning magnetic fields, an allphase magnetic field measurement system is developed, in which the electromagnetic induction method is used. The sensor consists of three 15 cm radius orthogonal magnetic loops. The data is recorded by an oscilloscope with high speed and high capacity. The pulse magnetic field waveform digital reconstruction method based on the full circuit equation is adopted in data restoration processing. The system is calibrated by a current generator with a maximum output of 6 kA in laboratory. The synchronized electric and magnetic observation data of two lightning flashes observed in the field experiment conducted in Conghua, Guangdong Province, is analyzed. It is found that the allphase magnetic field measurement system can reliably reflect lightning magnetic field change.