The demand for electronics requires solving the problem associated with the production of dilute magnetic semiconductors in a thin-film state based not only on wide-gap, but also on narrow-gap compounds, which are non-magnetic semiconductors in nature, and in which some atoms of the lattice are replaced by transition metal atoms, for example, Co. Therefore, it is of no less interest to obtain cobalt-doped thin-film PbS with a band gap width of 0.41 eV by low-temperature chemical deposition, which does not require complex equipment. Before trying to obtain substitutional solid solutions CoxPb1-xS, we have previously analyzed the ionic equilibria in the reaction system "Pb(CH3COO)2 - CoCl2 - Na3Cit - NH4OH - N2H4CS" which allowed us to establish that the prevailing complexes in the selected synthesis conditions are the hydroxocitrate complex of lead and ammonia complexes of cobalt, which prevent the rapid conversion of their salts into sulfides. In the pH region of hydrolytic decomposition of thiourea, the required amount of chalcogen ions (S2-) is supplied for interaction with active Pb2+ and Co2+ ions. Favorable conditions for the formation of solid solutions based on lead and cobalt sulfides that do not contain Co(OH)2 and Pb(OH)2 hydroxides, serve sufficiently high concentrations of sodium citrate (> 0.3 mol/l) and an aqueous solution of ammonia (> 3.75 mol/l) in the studied reaction mixture. The calculation results are presented in the form of three-dimensional graphical dependences in the coordinates “indicator of the initial concentration of lead salt (cobalt) - pH of the solution - ligand concentration”. Homogeneous layers of CoPbS with a thickness of ~450 nm and a crystallite size of ~200-300 nm, which proportion is ~60%, are obtained by chemical deposition from the calculated reaction mixture at temperature 353 K during 90 minutes on the glass substrates. An excess of metal ions is observed in the synthesized films compared to chalcogene with a cobalt content of 0.1 % at. in films obtained at the minimum concentration of cobalt chloride in the reactor.