A controllable arc suppression coil compensation device based on DSP TMS320F2812 is designed in the paper for the safe hidden trouble of neutral non-grounded way and the disadvantage of the old arc suppression coil in 10kV power grid at present. The improved extreme value method is used to measure the earthing capacitive current online, recognition of operating condition of power gird and fault type can be judged according to the neutral point displacement voltage, thyristor secondary capacitance-adjustable is used to achieve dynamic tuning, a control strategy combined over compensation with full compensation is used in this design. The result suggests that the system can realize functions such as accurate on-line measurement of capacitive current and automatic compensation for the earthing capacitive current, the device has high reliability and a good application prospect.