The structure and characteristics of CdTe thin films are dependent on the whole deposition process in closed-space sublimation system (CSS) in working atmosphere of Ar and O2. It is helpful for preparation of thin and compact CdTe thin films with fine photoelectric characteristics to study the heat exchange and mass transportation in CSS process. Here, the physical mechanism of CSS is analyzed, the temperature distribution in CSS system is measured, and the dependence of preliminary nucleus creation on increasing-temperature process and pressure is studied. The results indicate that the samples depositing in the different pressure are all cubical structure of CdTe with the diffraction peaks of CdS and SnO2∶F. With the gas pressure increasing, the crystal size of CdTe decreases, the transmission of the thin film goes down and the absorption side shifts to the short-wave direction. So the increasing-temperature curve has been optimized, and with the analysis integrated solar cells of better conversion efficiency in configuration of SnO2∶F/CdS/CdTe/Au are achieved.