Leptomeningeal metastasis (LM) is a rare yet devastating complication of solid tumors, frequently occurring in patients with lung cancer, breast cancer, or malignant melanoma, with an incidence of approximately 1%-5%. Diagnosis remains difficult, prognosis is poor, and no standardized treatment currently exist. Intrathecal administration, as a therapeutic approach, enables the direct delivery of drugs into the subarachnoid space, thereby increasing local drug concentrations. Conventional intrathecal chemotherapeutic agents primarily include methotrexate (MTX), cytarabine, and thiotepa. In recent years, with advances in drug development, a variety of novel chemotherapeutics, targeted agents, and immune checkpoint inhibitors (ICI) have gradually been introduced into intrathecal therapy. Furthermore, in-depth investigation into the pathogenesis of LM, along with the development of diagnostic techniques such as detection of circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) in cerebrospinal fluid (CSF) is offering new opportunities for LM diagnosis and therapeutic strategies. This review provides a comprehensive summary of the current diagnostic approaches and research progress in intrathecal treatment for LM.