The synthesis of a new ligand, m - bromobenzenediazoaminoazoben zene (m - BBDA )was carried out The reaction between m-BBDA and cadmium(II) was sensitive at PH over 12 andin the presence of emulsifier OP. Because of the high interference of excess of ligand β-correctiontheory was applied instead of the single wavelength method. This study gave the simpledetermination of the complex ratio, real molar absorptivity () and step or cumulative stabilityconstant (K).