To provide a method for producing a carbon fiber base material having excellent dispersibility of carbon fiber during base formation and excellent mechanical characteristics when made into a molded product.

The carbon fiber base material is produced by a production step having at least four steps of a step (I) for feeding a carbon fiber bundle to which 0.1-10 mass% of a water-soluble polyurethane and/or a water-soluble polyamide is attached, into a dispersion medium; a step (II) for preparing a slurry in which a carbon fiber constituting the carbon fiber bundle is dispersed into the dispersion medium; a step (III) for transporting the slurry to a step (IV); and a step (IV) for removing the dispersion medium from the slurry and forming a carbon fiber base material.