NOVELTY - Preparing carbon substrate comprises: forming oxidized carbon precursor fiber preweb (512) of oxidized carbon precursor staple fibers and binder staple fibers; impregnating oxidized carbon precursor fiber preweb with slurry, and drying resulting preweb to get oxidized carbon precursor fiber web; applying heat and pressure to oxidized carbon precursor fiber web, to cure thermosetting resin and press oxidized carbon precursor fiber web (510); and a carbonization process for heating oxidized carbon precursor fiber web, thus stabilizing and carbonizing oxidized carbon precursor staple fibers.    USE - The method is useful for preparing a carbon substrate for a gas diffusion layer of a polymer electrolyte type fuel cell.    ADVANTAGE - The method eliminates oxidation treatment process by utilizing carbon precursor staple fibers in an oxidized form and binder polymer staple fibers, thus preventing deviation and low processability of a carbon substrate product, and enhancing the workability while maintaining uniform thickness of the carbon substrate.    DETAILED DESCRIPTION - Preparing a carbon substrate comprises: forming an oxidized carbon precursor fiber preweb (512) comprising oxidized carbon precursor staple fibers and binder staple fibers; an impregnation process for impregnating the oxidized carbon precursor fiber preweb with a slurry including a thermosetting resin and carbonaceous fillers, and drying the resulting preweb to obtain an oxidized carbon precursor fiber web; a curing process for applying heat and pressure to the oxidized carbon precursor fiber web, which has been impregnated with the thermosetting resin and the carbonaceous fillers, to cure the thermosetting resin and press the oxidized carbon precursor fiber web (510); and a carbonization process for heating the oxidized carbon precursor fiber web in an inert atmosphere, thus stabilizing and carbonizing the oxidized carbon precursor staple fibers to obtain a carbon substrate. INDEPENDENT CLAIMS are also included for:    (1) a carbon substrate for a gas diffusion layer of a polymer electrolyte type fuel cell, prepared by the method of preparing a carbon substrate; and    (2) a system for manufacturing a carbon substrate for a gas diffusion layer of a polymer electrolyte type fuel cell, comprising: a preweb forming device for forming the oxidized carbon precursor fiber preweb; an impregnation device (210) for impregnating the oxidized carbon precursor fiber preweb with the slurry and drying the resulting preweb to prepare an oxidized carbon precursor fiber web; a curing device (310) for applying heat and pressure to the oxidized carbon precursor fiber web to cure the thermosetting resin and press the web; and a carbonization device (410) including a carbonization furnace for heating the oxidized carbon precursor fiber web in an inert atmosphere, thus stabilizing and carbonizing the oxidized carbon precursor staple fibers to obtain a carbon substrate.    DESCRIPTION OF DRAWING(S) - The figure shows a process flowchart of a method of preparing a carbon substrate.    Impregnation device (210)    Curing device (310)    Carbonization device (410)    Web (510)    Preweb (512)