In this paper, the method for forming the isochromatic dye ion-pair was described, and the mechanism and the types of the association of the ion-pair studied. The isochromatization of the associated reaction and the solvent effect were discussed by the electron theory with the absorption spectrum and energy diagram. The results of the extraction spectrophotometric method of the isochromatic dye ion-pairs were shown in a table, indicating the high sensitivity of the isochromatic dye ion-pairs. It is proven that the method of the extraction spectrophotometry, the flotation spectrophotometry and the extraction fluorometry was of high and superhigh sensitivity.