Atomic Force Microscopy (AFM) is widely used in morphology characterization of materials on nanometer and sub-micron scales. However, distortions universally exist in AFM images due to geometrical interaction between the sample surface and the limited size tip. Correction factors for AFM images are given in the paper based on a simple mathematical model. The results reveal that the correction factors are related with the distribution of the particles (compacted or dispersed). The distortions can cause bigger images than the real sizes using commercial pyramidal tips and the distortions are deflation under certain conditions as well. The distortions of the images are affected by the shape of the AFM tip and circumstance of the particles. The results are compared the experimental data.