The experimental results of absorption, luminescence and excitation spectra in both bare and coated SnO2 Nanocrystals are presented. It is found that the absorption edge shifts to the longer wavelength as the particle size decreases when the SnO2 nanocrystals are coated by a layer of organic moleculae, which is inconsistent with that of the bare SnO2 nanocrystals. It is demonstrated that the size and surface situations of nanocrystals great ly affect their spectroscopic properties. The experimental data are discussed in terms of the quantum confinement effects and dielectric confinement effects.