Abstract: Aiming at the unintended virtual inertia problems in the multi-converter DC systems based on the analogous virtual synchronous generator（AVSG）, a general analysis method for virtual inertia of the multi-converter DC systems is proposed, which effectively corrects the system-level external characteristics of the equivalent AVSG. Firstly, multiple control loops of AVSG are equated to one equivalent control loop of AVSG, and an equivalent single AVSG model of the DC system is established.Secondly, a system-level virtual inertia evaluation method is proposed to evaluate the system-level virtual inertia from the perspective of frequency-domain response characteristics of the output impedance of the equivalent single AVSG model. Thirdly,the influence of the voltage proportional-integral（PI） control parameters on the virtual inertia characteristics is discussed. And the coordinated design between the voltage PI control parameters and the virtual inertia coefficients is carried out. Finally, a switching model of the multi-converter DC system is built on the PLECS simulation software and RT-BOX hardware-in-the-loop experimental platform. The effectiveness and feasibility of the equivalent single AVSG model and the coordinated design of control parameters are verified in various experimental conditions.