Thermoelastic damping is a basic energy dissipation mechanism in the resonator, which determines the performance limit of high Q resonator. Testing the mass suspension support beam is difficult to solve analytically due to the variation of the cross section. Studies have shown that the classical L-R theory can be applied to the structure after the mass rigidity assumptions, yet the assumptions with respect to calculation error caused by the actual device is inconclusive. To solve this problem, a comparative analysis between the L-R calculation and ANSYS finite element analysis method was used to compare the first-order intrinsic frequency and the calculated error of thermoelastic damping coefficients at this frequency when the scales of the support beam and mass block were varied respectively. The results show that the calculation error of L-R theory is too large to calculate thermoelastic damping coefficient of mass suspension beam structure accurately, but it can estimate the change trend of thermoelastic damping effectively when the scale changes.