Decreasing CdS thickness is one of the effective ways to improve the conversion efficiency of CdS/CdTe solar cells. In order to eliminate the adverse effects of the decrease in CdS thickness on the performances of the devices, it is necessary to introduce a buffer layer between CdS and front electrode layer. The un-doped SnO2thin films, as a buffer layer, were deposited on SnO2:F thin film by magnetic reactive sputtering. Then the composite film was annealed at 550 ℃ in N2/O2=4 ∶1 ambience for 30 minutes. The morphology, structure and optical properties of the composite film before and after annealing were studied by AFM, XRD, UV-Vis and the electrical properties were analyzed, respectively. As a result, the crystal lattice parameters of un-doped SnO2 films matched those of the substrate, so the un-doped SnO2 films, which had an obvious preferred orientation along (110) plan, had the same structure as the substrate materials. This implied that there was no lattice mismatch. After annealing, the surface topography and electricity uniformity were improved, higher than 80% transparency was obtained, and resistance increased to meet the requirements of the buffer layers. Finally, continuous and homogeneous SnO2:F/ SnO2 composite thin films have been obtained, which were very suitable for CdS/CdTe cells.