We report the electrostatic properties of few-layer Bi2Te3 and Bi2Se3 nanoplates (NPs) grown on 300 nm SiO2/Si substrate. Electrons and holes are locally injected in Bi2Te3 and Bi2Se3 nanoplates by the apex of an atomic force microscope tip. Both carriers are delocalized uniformly over the whole nanoplate. The electrostatic property of topological insulator Bi2Te3 and Bi2Se3 nanoplates after charge injection is characterized by Kelvin probe force microscopy under ambient environment and exhibits an ambipolar surface potential behavior. These results provide insight into the electronic properties of topological insulators at the nanometer scale.