Potential Transformers (PT) are very important devices of monitoring the states of power system. The ferroresonance causes long-time over-voltage due to the saturation of the PT ferromagnetic inductors. To solve this problem, an intelligent suppression device of PT ferroresonance based on ARM and DSP is proposed. The DSP chip uses fast Fourier transform algorithm to analyze the distribution network voltage and judge the generation of ferroresonance, and then communicates with ARM chip. The ARM chip controls the switch of damping resistance to complete the suppression of ferroresonance and display / store / upload the relevant ferroresonance information. The device can accurately and quickly detect whether the ferroresonance occurs and rapidly suppresses it and records the information of it at the same time by making full use of the computing power of DSP and the control ability of ARM.