Abstract: Thermal runaway in the all-solid-state lithium battery (ASSLB) represents a primary bottleneck for technological evolution because of the violent exothermic characteristics associated with high energy density. A multi-level summary of research progress on the thermal runaway characteristics of ASSLB across the material, interface, and overall cell levels is provided, alongside a systematic analysis of the intrinsic correlations among these hierarchies. First, the potential exothermic reactions of ASSLB thermal runaway and its staged evolution from triggering to runaway are analyzed. Second, from the material level, the comprehensive performance, thermal decomposition temperatures, and research status of major solid-state electrolyte (polymer, oxide, and sulfide) are summarized. Then, the causes of thermal runaway at the interface between solid-state electrolyte and positive/negative electrodes are elucidated, and the research progress on the thermal runaway characteristics of mainstream electrode materials and solid-state electrolyte is introduced. Finally, the research progress of thermal runaway at the battery level is outlined, and the current prevention and control strategies for ASSLB thermal runaway are reviewed. The result indicates that polymer solid-state electrolyte possess good processability but limited thermal stability; oxide solid-state electrolyte exhibits excellent thermal stability but high interfacial impedance; sulfide solid-state electrolyte, despite high ionic conductivity, suffers from poor thermal stability and a tendency to generate toxic gases. The coupling between lattice oxygen release from the cathode and interfacial reactions is the core mechanism leading to the drastic temperature rise. Based on this, it is proposed that a cross-scale evaluation framework from material thermal stability to cell/module thermal safety should be constructed, and that proactive early warning strategies integrating in-situ sensing and intelligent algorithms should be developed, so as to promote a paradigm shift in ASSLB thermal safety from passive protection to active management.