The effect of CdS thickness and CdTe resistivity on short-circuit current, open-circuit voltage, fill factor and cell efficiency is studied in this work. The results have been carried out based on the optical losses (reflection and absorption) and recombination losses (front and back) under certain parameters of the absorber layer. It hs been found that the optical losses decrease with reducing the thickness of CdS layer. At CdS thickness of 100 nm, the contribution of optical and recombination losses is about 35% where the recorded current density is 20.1 mA/cm-2. With further decrease in CdS thickness up to 70 nm, the short-circuit current density increases up to 21.1 mA/cm-2 where the contribution of these losses is about 32%. The output power, open-circuit voltage and fill factor of CdS/CdTe solar cell are determined from the J-V characteristic. It has been found that these parameters increase with decreasing the resistivity of CdTe absorber layer and thinning the CdS window layer. The maximum cell efficiency of 16.5 % is obtained at CdTe resistivity=0.1 Ω cm and CdS thickness=70 nm.