Abstract: Kelvin probe force microscope (KPFM) can measure the surface contact potential difference (CPD) between the probe and the sample using Kelvin method. And the surface topography image and CPD can be obtained simultaneously. The CPD of both the as-deposited and annealed CdTe films have been measured by KPFM. High resolution KPFM measurements on CdTe films revealed interesting insights into the subtle variations in CPD at GBs. It is great significant for the analysis of carrier transport at grain boundaries and inside grains and interface passivation of polycrystalline semiconductor thin films. KPFM is an atomic force microscopy based derivative with high resolution. High resolution and subtle sensitivity make it suitable to analyse the nanostructure of polycrystalline semiconductor thin films.