The Li metal anode possesses the high specific capacity and the minimum reduction potential known as the renaissance of high-energy-density battery. However, the security problems brought by uncontrolled Li dendrites have hindered its development. Integrating the Li metal anode with non-flammable solid-state electrolytes (SSEs) provides a promising approach to solve the problem of Li dendrites and achieve safe Li metal batteries. However, recent studies indicate that Li dendrites still occur in the interior of inorganic SSEs, although the high mechanical strength of inorganic SSEs can resist dendrite growth in theory. In this review, the main causes of Li dendrites within inorganic SSEs are summarized. Combined with advanced characterization techniques and theoretical calculations, theoretical models of Li dendrite growth within SSEs are clarified. Furthermore, various strategies for suppressing Li dendrites are comprehensively summarized. Finally, the research prospects of dendrite-free all-solid-state Li metal batteries are evaluated.