In the process of detecting the concentration of trace cobalt ions in the high-concentration zinc solution by spectrophotometry, because chemical properties of Zn(Ⅱ) and Co(Ⅱ) are similar and the concentration of base ion is too high. Those facts lead to the overlap of the spectrum of Co(Ⅱ) and Zn(Ⅱ) which most of the spectral signals of Co (Ⅱ) are masked by the spectral signals of Zn(Ⅱ), strong nonlinearity of absorbance and concentration, and poor additivity in mixture solution in the partial wavelength. Thus it is difficult to determine the concentration of cobalt by the whole band information. In this paper, the interval-correlation coefficient-PLS is proposed to select the wavelength of the ultraviolet and visible spectrum of the solution and then establishes the absorbance-concentration model. Firstly, experiment was designed to obtain spectrum of Zn(Ⅱ) and Co(Ⅱ) mixture; Secondly , evaluation indicator-the predicted root mean square error was used to extract and optimize feature from full-spectrum data, which reduced masking effect of the high-concentration Zn(Ⅱ) and removed blank information.; Then the correlation coefficient method was adapted on the analysis of absorbance matrix in sensitive region of cobalt to select wavelength points detailed. The points selected finally could retain cobalt sensitivity and linearity in maximum degree; Finally, the partial least squares(PLS) model was established by the selected wavelength point to compute the concentration of Co(Ⅱ). The proposed method was compared with full band PLS, iPLS, MCUVE-PLS and CARS-PLS, and the result showed that with the proposed method the number of selected wavelength points respectively decreased 89.1%, 40%, 72.3% and 81.7%, and accuracy under this model respectively increased 64.6％, 33.3%, 38.7% and 24.3% compared with other methods in the background of the high concentration of zinc solution. The maximum relative error was only 5.45 % and the average relative error was 2.21%. The proposed method can properly resolve the problem of detecting trace cobalt ion concentration in high-concentrations zinc solution.