Systemic administration of anticancer therapeutic agents remains a crucial strategy for clinical cancer therapy. However, poor drug accumulation at tumor sites and severe side effects to normal tissues induced by off-target effects lower their therapeutic efficiency and limit their deep application in clinical settings. How to overcome these issues has continuously raised concerns. Reportedly, injectable thermosensitive hydrogels are good carriers for local drug delivery systems, demonstrating a flowable and injectable sol state at room temperature, easily loading therapeutic agents with large loading contents. Under normal body temperature, these hydrogels are stimulated to undergo a phase transition to an immobile gel state, which serves as a drug reservoir at local injection sites. After intratumoral or peritumoral injection, the localized hydrogel reservoir shows a slow and sustained drug release behavior, and can also targeted deliver therapeutic agents to cancer cells instead of normal cells, improving the therapeutic efficiency and reducing systemic side effects. This review summarizes the development of injectable thermosensitive hydrogel systems, reviews the research application advances of these systems in different therapy strategies for cancer, discusses the present issues and awaits their future in clinical applications.