Based on ESAC (energy system analysis consortium) standard of the impedance analysis method, the impedance characteristics and stability for the voltage source converter based HVDC (VSC-HVDC) are analyzed. Firstly, an equivalent circuit of the VSC-HVDC system is established. The impedance characteristics of the VSC-HVDC system are analyzed by using a complex-frequency domain equivalent circuit. A practical stability criterion, based on ESAC standard to determine the stability of VSC-HVDC system, is proposed. Secondly, the Nyquist curves of the VSC-HVDC system under different PI control parameters are calculated and obtained in the complex-frequency domain. The stabilities of the VSC-HVDC system are verified through the Nyquist curves. Finally, the time domain electromagnetic transient simulation results of the VSC-HVDC system performed in PSCAD/EMTDC show that the stabilities of the VSC-HVDC system are similar to that produced in the complex-frequency domain, which further proofs that the presented stability criterion is suitable for stability analysis of the VSC-HVDC system to select the optimal control parameters.