A new dual-wavelength superposition absorption spectrometry was established for the rapid and accurate determination of metoprolol tartrate in drug.In pH 4.55 acidic Tris-hydrochloric acid media and 586 nm-740 nm,metoprolol tartrate reacted with chlorophosphonazo Ⅲ to form an ionic association complexes with two obvious positive absorption peak.The maximum positive absorption wavelength located at 614 nm,and the second largest positive absorption wavelength was at 664 nm.The apparent molar absorptivity(κ) were 6.03×104 L/(mol?cm)(614 nm) and 5.37×104 L/(mol?cm)(664 nm),respectively.Metoprolol tartrate obeys Lombard Beers law in the range of 0.2-8.6 mg/L,and the detection limits were 0.13 mg/L(614 nm) and 0.15 mg/L(664 nm),respectively.When the double wavelength superposition absorption spectrometry was used to determine the concentration of metoprolol tartrate,its apparent molar absorptivity(κ) could be achieved to be 114×105 L/(mol?cm),and the detection limits was 0.072 mg/L.The optimum chromogenic reaction conditions,effects of the coexistence material and absorption spectral characteristics were studied.It was found that the apparent molar absorptivities for the single wavelength and dual wavelength superposition absorption spectra of the reaction system were 5.37×104-1.14×105 L/(mol?cm).The method was applied in the determination of the content of metoprolol tartrate in commercially available metoprolol tartrate medicine with the spiked recoveries and RSD(n=6) found were in the ranges of 98.0%-101%and 1.8%-2.3%,respectively.