The invention discloses a gold nanoparticle used for detecting a heavy metal ion, and a preparation method thereof. The technical method is characterized in that an amino and/ or carboxyl on an organic compound can be used for forming a strong hydrogen bond function on the basis of an agglomeration mechanism, a strong [Pi]-[Pi] accumulation function is formed through a benzene ring on the organiccompound so as to cause gold nanoparticle agglomeration, the color of solution changes to cause the change of the peak position and the adsorption intensity of the resonance absorption peak of the surface plasma of the gold nanoparticle, the change of the peak position and the intensity of the adsorption peak can be seen directly with eyes and ultraviolet, so that whether a sample contains Cd<2+>,Ba<2+> and Pb<2+> ions can be quickly detected, the concentrations of the ions can be quickly detected, and therefore, the quick detection of the Cd<2+>, Ba<2+> and Pb<2+> ions in the sample can be realized. The technical has the advantages of being simple in operation, low in cost, wide in applicable range and the like.