Thermal effect on the equivalent spring constants of double-clamped beams (bridges) with two kinds of mass arrangements including central mass and side mass were studied by theoretical analysis and finite element simulation. An equation to describe the change of the equivalent spring constants of beams due to temperature variation was derived and the equivalent spring constants from simulation results of the fundamental vibration frequency and the displacement under a static load were obtained respectively by the finite element analysis. Results show that the temperature variation has an important effect on the equivalent spring constants.For the fundamental vibration frequency,there are a good agreement between the derived equation and the vibration simulation results for the both structures. For the displacement under a static load, the asymmetry in mass arrangement results in the bending of the beam when temperature shifts,and the bending causes a displacement of the mass to the side. As a result, the asymmetric arrangement of mass changes the initial displacement of mass when temperature varies, which would cause the changes of output signals for Micro Electro Mechanic System (MEMS) sensors or actuators.