Deep caries occurs when caries progresses to the deep dentin layer, and further progression has the risk of pulp exposure, which may affect pulp vitality and tooth longevity. Currently, there are no objective standards for the diagnosis of deep caries. In addition, traditional therapy for deep caries emphasizes complete debridement of the decayed tissue, resulting in an incremental high risk of pulp exposure. There are different views on how to deal with the remaining dentin after caries removal, and root canal treatment is often adopted directly after pulp exposure. In recent years, due to advances in dental pulp biology, bioactive pulp-capping materials, and clinical evidence-based medicine, the principle of deep caries treatment has shifted to pulp protection. Based on the latest international research progress, evidence-based medicine and expert consensus, we present a series of advancements in this article, including the terminology of deep caries, pathological changes and defense mechanisms of the pulp close to the deep caries, treatment principles of deep caries, technical strategies for carious tissues removal, and the decision-making of treatment protocols after pulp exposure, with the aim of enhancing the understanding of deep caries among dentists, as well as providing a reference for the clinical diagnosis and treatment of deep caries.