Objective:To evaluate the significance of copy number variation (CNV) and metagenomic next-generation sequencing (mNGS) of cerebrospinal fluid (CSF) in the diagnosis of meningeal carcinomatosis (MC).Methods:Ten patients with MC diagnosed in the Department of Neurology of Peking Union Medical College Hospital from March 2022 to June 2022 were consecutively enrolled in this study. The patients were diagnosed according to the criteria of the Chinese expert consensus on the diagnosis of MC by the Chinese Society of Infectious Diseases and Cerebrospinal Fluid Cytology, and the diagnosis of MC was confirmed by CSF cytology. The control group included 10 patients who were diagnosed as autoimmune encephalitis or viral encephalitis. CSF mNGS and CNV analysis were performed simultaneously in all the patients.Results:Of the 10 patients with MC, 6 had lung adenocarcinoma, 4 had breast cancer. CSF mNGS and CNV analysis detected large CNV in 8 of 10 patients with MC, including 4 patients with breast cancer and 4 patients with lung cancer. The results of pathogenic microorganism analysis of CSF mNGS in all the patients were negative. Meanwhile, large CNV was not detected in the control group.Conclusions:CSF CNV can serve as a diagnostic marker for MC. The combination of mNGS and CNV analysis has demonstrated a high positive rate in the diagnosis of MC. The dual-omics analysis of pathogenic microorganisms and CNV has been proposed as a potential strategy to further expand the clinical utility of CSF mNGS in the realm of auxiliary diagnosis.