Chemical bath-deposited (CBD) thin film CdS has been widely used as buffer and n-type window layer in CdS/CIGS and CdS/CdTe thin film solar cells. Annealing of CBD CdS assigns to the layers required concentration and mobility of electrons, crystallinity, structural stability and perfect ohmic front contact in TCO/CdS interface. Annealing of CBD CdS assigns to the layers required concentration and mobility of electrons, crystallinity, structural stability and perfect ohmic front contact in TCO/CdS interface. But always annealing reduces band gap (Eg) of solution-deposited CdS and lowers current density of the CdS/CdTe PV device due to optical absorption within the CdS layer. We have studied systematically dynamics of changes in CBD CdS/glass thin film structural, optical and electrical properties in annealing process in H2 anbient at normal pressure in pre-heated ceramic tubular furnace. We will present electrical, x-ray diffraction (XRD), photoluminescence and visible optical spectroscopy characterization results of annealed CBD CdS/glass thin films. The films were deposited from ammoniacal 1 mM dilute solution of CdSO4 with thiourea. On the basis of acquired results we propose an hypothesis about substitutional incorporation of OH group on S site in CdS lattice in deposition process and that (OH)S complex defect acts as a donor defect like Cl and is responsible for changes of thin film CdS electrical, optical and structural properties in the annealing process. Cubic CdS is stable and prevalent phase in CBD CdS thin films even at 450 °C.