This paper presents a “combined” circuit model to simulate non-linear behaviors of a no-insulation (NI) high temperature superconductor (HTS) coil. The key idea is a selective use of either the lumped circuit model or distributed depending on an operating condition. When the NI coil current is below its critical current, the radial leak currents through turn-to-turn contacts may be assumed to be uniformly distributed over the entire coil, thus, the lumped circuit model may suffice to analyze the NI behaviors. When the coil current increases beyond the critical current, the distributed model plays the role to simulate the spatial distribution of currents, both radial and azimuthal. By limiting the use of the time-consuming distributed model only for the post-quench part, the combined model enables substantial reduction in calculation time without sacrificing simulation accuracy. To verify the validity of the combined model, an over-current charging test of an NI HTS coil was simulated with the lumped, distributed, and combined models. The simulation results of the combined model are barely discernible from those of the distributed model, and agreed well with the measured ones as well. The results validate the combined model for more efficient simulation of an NI HTS coil.