Abstract: The authors synthesized some azomethine dyes derived from 3-methyl, 3-amino, 3-anilino, 3-benzoylamino, and 3-phenylureido-pyrazolone oompoutods. The model systems for study are the above dyes in n-butyl acetate.The formula R_E=ε_y/ε_x, where ε_x and ε_y can be measured, was defined as the experimental value of unwanted absorption. The modified PPP-CI method was programmed for calculating the structural models of dye molecules. The formula R_T=f_y/f_x was defined as theoretical value of undesirable absorption, where f_x and f_y are oscillator strength.It was found that a very good linear relationship exists between R_E and R_T (the linear correlation coefficient r=0.99). The main result of this paper showed the theoretical formula of unwanted absorption can be expressed as R=0.349R_T+0.051.