To provide a method of preparing a lithographic printing plate which is safe, exhibits excellent developing property and processing ability, and enables processing with one solution by processing after image exposure, a negative lithographic printing plate precursor having an image-recording layer containing (i) a sensitizing dye, (ii) a photopolymerization initiator, (iii) an addition polymerizable compound having an ethylenically unsaturated double bond, and (iv) a binder polymer on a hydrophilic support with an aqueous solution containing a carbonate ion, a hydrogen carbonate ion and a water-soluble polymer compound.