In this paper, we present a simulation analysis on thermoelastic damping in single-crystal silicon nanowire resonators. The silicon nanowires are beams with rectangular cross-section. The thermoelastic damping characteristics of the resonator are investigated through estimating the quality factor as functions of width to height aspect ratio and cross-section of the resonant beam. The length of resonant beam is 1µm kept to be constant. The quality factor of the resonator is calculated by solving the coupled thermoelastic equations by finite element method.