This study investigates the post-arc sheath growth dynamics in vacuum interrupters under DC interruption conditions, focusing on the effects of plasma distribution and interruption parameters. This paper characterizes the spatial distribution of metal atoms and ions prior to current zero through emission spectroscopy experiments using a demountable vacuum interrupter. The results reveal distinct axial distribution patterns for atomic and ionic spectral lines, presenting enhanced intensities near the cathode and anode regions and uniform but lower values in the interelectrode gap. An enhanced Continuum Transition Model (CTM) is developed, incorporating residual micro-particle distributions to improve computational accuracy for sheath growth. The model demonstrates that metal vapor ionization significantly retards sheath growth while increasing electric field strength and power density at the cathode surface. Moreover, the study systematically analyzes the influence of key operational parameters, including arcing duration, interruption current, and current changing rate (di/dt), on post-arc sheath formation. The findings provide critical insights into optimizing interruption conditions to enhance dielectric recovery strength and improve the reliability of vacuum interrupters in DC systems.