Stability is an important concern for the three-phase grid-connected converter(GCC) connected to a three-phase voltage source converter(VSC). However, the traditional grid-connected converter with parameters designed for grid connection requirements may have the problem of current oscillation when three-phase ac voltage is supported by voltage source converter. In this paper, the output impedance of VSC with double-closed-loop control of voltage and current is established. Moreover, the influences of impedance and controlled power on power system stability are analyzed by Bode diagram. Finally, the control parameters are redesigned and verified on a 100-kW three-phase ac system.