Abstract: The present invention relates to a method for synthesis of o-diphenylphosphinobenzoic acid which includes the steps as follows: using chlorodiphenylphosphine as starting material, chlorodiphenylphosphine and alkali metal are added to the solvent to conduct cracking, which produces a diphenyl phosphine alkali metal salt, then o-chlorobenzoic acid salt or o-chlorobenzoic acid ester is added to conduct coupling reaction to produce diphenylphosphinobenzoic acid salt or diphenylphosphinobenzoic acid ester, o-diphenylphosphinobenzoic acid is obtained after hydrolysis. o-diphenylphosphinobenzoic acid can be prepared under atmospheric pressure at temperature above 0° C. by using the present method. The method is safe and stable to operate and can save a lot of energy, thus being suitable for large-scale production.