A finite element simulation software Comsol Multiphsics was employed to build threedimensional bulk acoustic wave(BAW) resonators model. The influences of different structure and materials on the thermal characteristics of the BAW resonators were investigated. The calculation results revealed that the solid mounted resonators(SMR) had better thermal reliability than that of film bulk acoustic resonators. Adding SiO2 layer into the SMR will increase the steadystate temperature of 7 ℃.The highest steadystate temperature will increase rapidly with the decrease of the resonant area of SMR. The steadystate temperature decreased greatly when the high thermal conductivity materials are used to replace materials of low thermal conductivity in SMR.