For a sudden contaminant release in an indoor environment, source localization can provide critical information for preventing and mitigating indoor air pollution and its related health and security problems. Considerable research has focused on locating indoor contaminant sources with instantaneous or constant release rates; however, few studies on locating indoor sources with time-varying release rates have been reported. This study proposed a multi-robot active olfactory method for promptly locating time-varying sources in 3D indoor environments. The method extends our previously proposed method for 2D indoor environments by redefining and reprogramming it in a 3D coordinate system and proposing a 3D source declaration algorithm. Via more than 200 numerical experiments in 3D indoor environments with mixing, displacement, and piston ventilation systems, the method was fully demonstrated and validated. The results show the applicability and reliability of the method and reveal the effects of space style, ventilation mode, source release rate, source location, and obstacle layout on source localization.