Abstract: The inverter interfaced distributed generation (IIDG) is connected to the power grid through grid-connected inverters, and the fault current characteristics are significantly different from traditional equipment, posing challenges for fault protection in the distribution network. The positive and negative sequence separation algorithm based on T/4 delay is widely used in the grid-connected converter control system. However, the effect of delay link on the transient fault current characteristics has not been fully studied. Therefore, on the basis of sorting out the transient response link of the converter fault, the mathematical models of the converter topology and the control system with positive and negative sequence separation links were respectively established firstly, and the delay link was linearized by Pade approximation. Furthermore, a closed-loop model for the transient fault current of grid-connected inverters was established, and the impact of delay link on the transient fault current characteristics was analyzed. Finally, the correctness of the proposed calculation method and analysis results were verified by the MATLAB/Simulink simulation. The calculation error of the transient current calculation method proposed in this paper was below 1%.The research shows that the content of transient current can reach more than 2 times the rated current. The delay link will result in measurement errors between the measured value and the actual value, and the input of this measurement error into the current closed-loop will cause new features such as positive and negative sequence dq axis current oscillation, and temporary increase in low harmonic content.