In the present paper the author has elaborated a model, which provides prognostication forecasting of solid solution Cd xPb 1-xS composition at co-precipitation of individual lead and cadmium sulphides. It has been shown that content of CdS in a solid solution has extreme characteristics depending on lead Pb 2+ and cadmium Cd 2+ ion concentration in a reactor. Satisfactory correlation of simulation results with experimental data, obtained by X-ray analysis of the synthesized films, has been proved.