In this paper, a flexible surface acoustic wave device with “lithium niobate /benzocyclobutene(BCB)/ polyimide” structure is simulated and studied by finite element simulation method. The results show that the stable Rayleigh wave cannot be excited when the thickness of lithiumniobate(LN) is between 0.06λ~0.8λ, while outside this interval, Rayleigh waves can be excited. When the temperature increases, the resonant frequency of the device decreases. The calculation results show that the change of sound velocity with temperature is the main reason, which is greater than the frequency shift caused by thermal expansion. The simulation results in this paper provide a theoretical basis for the reasonable selection of piezoelectric film thickness and mechanical properties of substrate materials when designing and fabricating flexible surface acoustic wave devices.