The quasicontinuum (QC) approach is extended for multiscale analysis of silicon nanostructures at finite temperature. In this approach the constitutive relation for the finite temperature solid systems under isothermal conditions is determined by using the Helmholtz free energy density of the representative atoms. The static part of the Helmholtz free energy density is obtained directly from the interatomic potential while the vibrational part is calculated by using quantum-mechanical lattice dynamics theory. Specifically, we investigate two quasiharmonic models, namely the local quasiharmonic model and the quasiharmonic model in the reciprocal space, to compute the vibrational free energy. Using the finite temperature QC method, we compute thermodynamic and elastic properties of Tersoff silicon. We also compute the mechanical response of silicon nanostructures for various external loads and the results are compared with molecular dynamics simulations.