A presetting and following-setting compensation mode with auto-switchable and adjustable Petersen-coil connected in parallel with a fixed reactor is implemented for distribution systems with high three-phase asymmetry， and a capacitive current real-time measuring technique is studied. In order to improve the measurement accuracy， the FPGA chip and high precision crystal are adopted to measure the phase difference between the injected signal's voltage and current， and the linear interpolation algorithm is employed to accurately calculate the resonance frequency of the distribution system. The measuring and control device for Petersen-coil automatic tuning is developed， and capacitive current accurately measuring is implemented. Simulation and test results show that the measuring technique is highly accurate and measuring range wide and simple. It can be applied in distribution systems with Petersen-coil presetting and prefollowing-setting.