Abstract: A virtual synchronous generator (VSG) has the similar output characteristics to the traditional synchronous generator (SG), which can provide necessary the voltage and frequency support for a power grid. However, under fault conditions, the VSG may suffer from the transient power angle instability as the SG does, and the VSG cannot withstand the excessive current during the fault. Due to the weak overcurrent capacity of the VSG, it is generally necessary to set a corresponding fault current limitation loop for it. After the current limitation loop is added, the transient characteristics of the VSG are changed with the complexity of its transient analysis increased. At present, the influence of the current limitation loop on the transient stability interval of the VSG has not been made clear. Based on the analysis above, this paper, considering the qualitative influence of the current limitation loop on the transient stability of the VSG, obtains its transient performance during a whole fault process. Then, with the help of the mathematical analysis methods such as the Runge-Kutta algorithm and the least square method, the critical clear angle (CCA) and the critical clear time (CCT) under different overcurrent coefficients and fault depths are obtained to achieve the quantitative description of the VSG transient stability interval, providing a guidance for the actual operation of such power grids with relay protections. Finally, simulations and experiments have proven the correctness of the theoretical analysis and the accuracy of the description of the VSG transient stability interval considering the current limitation loop.