Most of existing impedance modeling work for Virtual Synchronous Generator (VSG) typically ignores the DC-side dynamics, which may deteriorate the accuracy of the stability analysis. To this regard, a VSG impedance model is developed in this paper taking into account the DC-side dynamics and associated control effect. First, the structure and control strategy of the VSG with DC-side voltage control is unfolded. Subsequently, the sequence impedance model of the VSG is established through a small-signal modeling approach. The accuracy of established impedance model is then validated with impedance sweep method and its impedance characteristics are also compared with the one without DC-side voltage control. The results demonstrate strong consistency between the theoretically derived impedance and the measured frequency response. The analysis based on the results indicates that DC-side dynamics can lead to considerable low-frequency phase shifts, thus posing potential low-frequency oscillation risks.