Thermoelastic damping （TED） is one of the key coefficients that determines the upper limit of the quality factor of the micromechanical resonator. In the past， the TED model was only suitable for fully covered multi?layer microbeam structures. However， due to the manufacturing process and actual functional requirements， complex structural forms represented by incompletely covered double?layer beams are more common. Based on Fourier's law of heat conduction， this paper derives an analytical model for the TED of the partially covered bilayer microbeam resonators with the heat conduction along the length and thickness directions. Meanwhile， numerical methods and experimental data are used to verify the effectiveness of the model. The effects of the thickness， length and position of the coating on the TED is also analyzed. The results provide a new idea for reducing TED by optimizing the length and position of the coating.