CdS/CdTe Thin film solar cells are grown in a homemade close-space sublimation system where the cell fabrication of p-n junction is carried out in a continuous, in-line process. The best efficiency achieved is about 11% (AM1.5). Another cell is prepared with the same procedure except for the n-CdS layer coated by sputtering(SP), achieving an efficiency of about 10% (AM1.5). Current density-voltage and external quantum efficiency measurements are analyzed and the solar cell performances are characterized. By the comparison between the practical fitted data and theoretical calculations, the method of improving CdS/CdTe solar cell efficiency, i.e., increasing the open-circuit voltage (Voc), short circuit current (Jsc), and fill factor (FF), is proposed.