It is used to measure the grounding resistance of large grounding grids. The instrument uses the different frequency multi-source method for measurement during one measurement. The computer controls the output frequency of the power supply and through computer data acquisition and data processing, the interference between the measurement leads is eliminated. . The instrument also uses hardware filtering technology and software filtering technology to reduce the error caused by power frequency interference to the measurement results, further improve the signal-to-noise ratio, and make the measurement results of the instrument more stable and reliable.