The study of physical properties of silicon nano-materials is very important for its application in semiconductor technology. Doping is beneficial to improving the physical properties of silicon nano-materials, it can improve the application value as well. Young's modulus of the crystal in the direction of [100] of the doped silicon nano-film is studied by an analytical model, which is based on the semi-continuum approach. In the model, the strain energy is obtained from the Keating strain energy model. The relationship between the Young's modulus and film thickness are also discussed. Results show that the Young's modulus decreases with the increase of the thickness of the silicon film, especially with the small size; the variation tendency of the Young's modulus of doped silicon films is similar to the pure silicon film. And the Young's modulus decreases as the doping concentration decreases for different doping position. Neither the doping concentration nor the doping position, it is the thickness that shows the most important effect on the Young's modulus of the doped silicon nano-film. Findings in this paper may serve as a reference for similar study, and can offer a totally new idea of the doped monocrystalline silicon materials as well.