This invention discloses a method for synthesizing 1-naphthalene sulfonic acid and / or sodium 1-naphthalene sulfonate. The method comprises: (1) dissolving naphthalene in solvent, adding appropriate 1-naphthalene sulfonic acid seed crystals, cooling to 0 minus or plus 5 deg.C, stirring, dropping chlorosulfonic acid within 1-2 h, and keeping at -2-8 deg.C for 1.5-3 h; (2) cooling to 0 minus or plus 2 deg.C, and filtering to obtain the filter cake of 1-naphthalene sulfonic acid; (3) washing the filtrate with water, phase-separating to obtain the solvent and water scrubbing acid (for producing high-performance naphthalene water reducer); (4) neutralizing 1-naphthalene sulfonic acid and the solvent with 5-15% NaOH, keeping at 90 minus or plus 5 deg.C for 10-30 min, phase-separating the neutralization solution to obtain sodium 1-naphthalene sulfonate aqueous solution, cooling to lower than 35 deg.C, crystallizing, filtering to obtain the filter cake of sodium 1-naphthalene sulfonate, and utilizing the filtrate to prepare NaOH solution. The method has such advantages as high sulfonation selectivity, low product isomer content, easy operation and no wastewater.