Leptomeningeal metastasis is a severe complication of advanced cancers such as lung and breast cancer. Due to the blood-brain barrier, systemic treatments are often ineffective, leading to poor prognosis. Intrathecal injection, as a local treatment method, bypasses the blood-brain barrier by delivering drugs directly to the subarachnoid space, thus increasing drug concentration in the central nervous system and reducing systemic toxicity. In addition to traditional chemotherapy drugs like methotrexate and cytarabine, newer agents such as pemetrexed, targeted therapies, and immune checkpoint inhibitors are being explored for intrathecal therapy, showing promising efficacy and safety in some patients. However, existing evidence is mainly based on small sample studies, and further prospective research is needed to validate their effectiveness and safety. This review aims to summarize the mechanisms, commonly used drugs, clinical advances, and efficacy of intrathecal injection in the treatment of leptomeningeal metastasis in non-small cell lung cancer.