The invention discloses a system and a method for detecting insulation of an electric automobile DC charging pile, and belongs to the field of electric automobile charging piles. The system comprises a bridge-type impedance network, a voltage conditioning circuit, an isolation unit, an A / D sampling unit, a main control unit, a communication unit and a fault alarm unit, wherein the bridge-type impedance network is used for detecting voltage information of the DC charging pile, and the voltage information is processed sequentially through the voltage conditioning circuit, the isolation unit and the A / D sampling unit and then sent to the main control unit; the main control unit calculates the voltage information processed by the A / D sampling unit so as to acquire a positive bus ground insulation resistance value and a negative bus ground insulation resistance value of the DC charging pile, the main control unit controls the fault alarm unit to alarm on the one hand, and on the other hand, the main control unit sends a calculated resistance value to an electric automobile DC charging pile control system through the communication unit. The system and the method disclosed by the invention are simple in circuit structure, reliable, high in precision, high in anti-interference ability and capable of effectively carrying out insulation detection on the electric automobile DC charging pile.