Aiming at the increasing test requirements for small current ground fault detection and protection devices, a simulation testing system for small current grounding fault based on digital simulation results was developed. Typical distribution systems that could simulate most kinds of the single-phase ground faults were built. The selection method of simulation step size was given. The Hochrainer model was used to simulate arc and the conditions of arc burning and extinguishing were improved. A high resistance earth resistance was connected to each phase to solve the problem that the Π-type equivalent model in ATP-EMTP could not simulate the ground conductance, so that the DC charge could be released after arc extinguishing. The availability of the test system was verified by comparing the simulated waveforms with the actual fault waveforms.