Intrathecal chemotherapy is one of the mainstay treatment options for leptomeningeal metastases. Pemetrexed is one of the first-line chemotherapeutic agents for non-squamous non-small cell lung cancer (NSCLC). Since 2017, intrathecal pemetrexed has shown good efficacy for patients with leptomeningeal metastases from NSCLC. It has been recommended as the preferred drug for intrathecal chemotherapy by the Chinese Society of Clinical Oncology (CSCO) guidelines. Tyrosine kinase inhibitors (TKIs) play a promising role in the treatment of non-small cell lung cancer patients with epidermal growth factor receptor (EGFR) mutations. Due to its small molecule properties, it can effectively penetrate the central nervous system barrier and deliver an effective antitumor effect. An international multi-center clinical study published in 2019 confirmed that double-dose of osimertinib showed significant improvement in leptomeningeal metastases from NSCLC with EGFR exon 19 deletion or exon 21 L858R/T790M mutation. It makes TKIs the mainstay of treatment for patients with EGFR-mutant NSCLC with leptomeningeal metastases. However, whether third-generation small molecule TKI drugs (e.g. 'osimertinib') combined with intrathecal pemetrexed could benefit patients with LM from EGFR- mutant NSCLC remains undetermined.