The invention discloses a luminol or isoluminol synthesizing method by a one-pot process. The luminol or the isoluminol synthesizing method by the one-pot process includes the steps of 1) enabling 3-nitrophthalic acid or 4-nitrophthalic acid as a starting material to react with urea in an organic solvent to obtain 3-nitrophthalimide or 4-nitrophthalimide; 2) enabling the 3-nitrophthalimide or the 4-nitrophthalimide to react with a hydrazine hydrate aqueous solution to obtain 3-nitrophthalhydrazide or 4-nitrophthalhydrazide; 3) enabling the 3-nitrophthalhydrazide or the 4-nitrophthalhydrazide to react with a reducing agent in the presence of a catalyst to obtain luminol or isoluminol. The luminol or the isoluminol synthesizing method by the one-pot process has the advantages of simplicity, convenience in operation, low cost, high yield and less pollution, and can be applicable to industrialized production.