The stability analysis of low-switching-frequency voltage-source converter(VSC) in weak grid is unintuitive and ineffective due to its large control delay, considerable grid impedance and phase-locked loop(PLL)’s asymmetry. To this end, an accurate complex-vector model of symmetrical PLL-synchronized VSC is established. Based on the obtained model, double-sided frequency analysis method is employed to describe the characteristics of entire system. Furthermore, this paper depicts the stability margin of VSC system clearly, and provides theoretical guidance for stability enhancement. Here, a phase correction scheme is also given to enhance system’s stability, and its effectiveness is verified with simulation results.