Abstract: Film bulk acoustic resonator (FBAR) force sensor is regarded as a new type of resonant sensor ,whose design is based on force-frequency characteristics of FBAR. This paper aims to analyze the force-frequency characteristics of FBAR that works in the longitudinal mode and adopts wurtzite AlN as piezoelectric thin film, whose resonance frequency shift results from the elastic constant under the stress load by taking an FBAR micro-accelerometer as an example. First, the stress distribution of the piezoelectric thin film of FBAR which integrated on FBAR micro-accelerometer under the inertial forces was obtained from applying the static simulation of finite element analysis. Then the maximum stress value selected as stress load, combining first principles to calculate the relation ship between elastic coefficient and stress of wurtzite AlN, so that the maximum variation of AlN elastic coefficient under the stress load can be predicted. Next, the resonance frequency with shift properties of FBAR micro-accelerometer are compared under different stress loads with the analysis result of harmonic response so as to predict the frequency characteristics and tendency of FBAR. By analyzing FBAR under the stress loads, its resonance frequency can be concluded to shifts to a higher one, and FBAR micro-accelerometer sensitivity is about kHz/g, which indicates the good linearity of acceleration increment-frequency shift characteristic curve.