Abstract: Based on the field-path combination method,the current and magnetic field distribution of the air-core reactor before and after the short-circuit between the turns are studied by MATLAB software programming.This study provides a theoretical basis for the magnetic field detection method of detecting the short circuit fault of the reactor through induction coil.The magnetic field detection method of the two sets of test coils proposed in the patent 2010-10217935.7 is improved to the multi-path test coil detection method.Taking a dry-type air-core reactor as an example,the signal acquisition and short-circuit signal detection were carried out using FPGA.It can be seen from the experimental results that the detection system can quickly and timely acquire the inter-turn short-circuit signal and issue an alarm,which verifies the effectiveness of the improved magnetic field detection method.