Based on existing test solutions of feeder automation, the transient simulation software PSCAD/EMTDC is employed to integrate with existing test platform to form a closed-loop test bench by the developing of user defined function modules. To streamline data exchange among PSCAD/EMTDC, test platform and DTU, a data relay method is used. The currents and voltages obtained from PSCAD/EMTDC can be injected into master station or DTU, at the same time the state of switches of tested distribution network shall be updated in PSCAD/EMTDC accordingly. The new test method could simulate various operation conditions and faults, especially for the earth fault. The new method has been applied to a testing distributed FA system, the results demonstrate the feasibility of this method.