Abstract: With the increasingly active engineering construction in mountainous areas these years, the giant remote gully disaster chain induced by landslide-debris flow transformation has attracted widespread attention for its superb motility and huge destructive power. Compared with the single hazard of landslide, the transformed debris flow has significantly increased in disaster scale, movement form, affected scope, and construction damage degree. Therefore, scientifically understanding the process and mechanism of landslide-induced debris flow is important to reduce the risk of remote gully disaster chain from the beginning, and subsequently, choose suitable mitigation measures. This study systematically reviews the concept, conditions, and mechanism of landslide-induced debris flow based on recent research achievements in the world. First, the concept of landslide-debris flow transformation is clarified by comparing it with the phenomenon of high-speed and long-runout landslides. Subsequently, we sort out the transformation conditions of landslide-induced debris flow from three perspectives of solid material, water source, and topography. We find the landslide can transform into debris flow only if it is satisfied with a combination of both three conditions. We further sort out the static and dynamic indicators that are used to classify landslides and debris flows from the microscopic scale. The results indicate a combination of both static and dynamic indicators may be the suitable choice to quantitatively the transformation process. Based on a large number of cases of landslide-induced debris flow, we also summarize two modes of landslide-debris flow transformation, which fall into static and dynamic transformation. The physical mechanisms are further discussed. Finally, we propose three key scientific challenges for landslide-debris flow transformation study: (1)Scientific and quantitative characterization of landslide-debris flow transformation processes; (2)Mechanism of the phase change when coupled solid, liquid, and gas in disaster; and (3)Critical conditions of landslide-debris flow transformation based on physical mechanisms. We further point out the relevant theories and methods for transformation mechanism study, and their feasibility in quantitatively characterizing the physical mechanism analysis of landslide-debris flow transformation process is also discussed.