Abstract: Multiple converters and negative impedance characteristics of constant power loads of DC microgrid will lead system instability. First, the equivalent input and output impedance of the system have been obtained. Based on the Nyquist stability criterion, a passivity based parallel impedance method has been proposed to determine the system voltage stability. The proposed method can transform the stability problem into the system passivity problem and its performance was compared with the traditional impedance ratio criterion. Secondly, in order to improve the stability of DC microgrid, an active damping control method based on the feed current of the DC converter is proposed. The design principle of the active damping parameters is given. PSCAD simulation results verify the effectiveness of the proposed method.