Disclosed is method of preparing a selenium carbon composite material and a use of the selenium carbon composite material in a cathode of a lithium selenium secondary battery. A battery formed with a cathode of the disclosed selenium carbon composite material has high energy density and stable electrochemical performance. The disclosed selenium carbon composite material can effectively shorten the migration distance of lithium ions during charging and discharging of the battery and improve conductivity and utilization of selenium after compounding carbon and selenium. Multiple batteries formed with cathodes of the disclosed selenium carbon composite material can be assembled into a lithium selenium pouch-cell battery having stable electrochemical performance and high energy density.