The existing line-to-earth capacitive current detecting system based on variable frequency method uses PWM inverter as variable frequency source, which has many constraints in practical use. This paper redesigns the detecting system. Each measure unit is constructed with double single-chip computer model and uses single-chip to control the DAC chip as the variable frequency source. The model experiment proves that the DAC type variable frequency source has better performance than the source based on PWM inverter. The system-on-chip of C8051F20 is in charge of the phase detection and communication function. The build of upper computer software is based on the C/S architecture. This detection system can detect the capacitive current within 10 seconds and the field experiment proves that the measuring error is under ±2%. This system can be directly applied to the preset arc suppression coil in medium voltage distribution network; it can also be applied to the post-set arc suppression coil after further designed.