The fault arc simulation and modeling is very important for the development of electrical equipment and the virtual analysis of power system operation. This paper studies the arc grounding fault modeling simulation based on real time digital simulator (RTDS). The mathematical model of the continuous system of Cassie arc is numerically approximated and converted into a numerical recursive model of the discrete system; a controllable Cassie arc element model is created in the RTDS’s CBuilder development environment. Through comparison with MATLAB standard model and experimental testing, as well as the neutral ungrounded system of single-phase arc grounding fault application experiments, the correctness and validity of the self-element model is validated. The arc model built in this paper fills the gap of RTDS simulation model, the method of modeling is universal, and it provides reference for similar research. The research results can be used in real-time arc fault simulation of power system and real time closed loop hybrid simulation of relay protection equipments. This work is supported by National Natural Science Foundation of China (No. 51567004).