Abstract: Theoretical study about mirror shows, in application range, transmissivity has a simple linear relationship with the axial stress to photonic crystal. Accordingly, a new structure accelerometer with axially deformed tiny beams was designed. Tiny beams are sensitive, so the sensitivity and frequency of free vibration of the structure will be increased significantly when tiny beams were in axial position. Using mirror triply periodic photonic crystal replace the original pressure sensitive resistor as the sensing element. Detecting the transmissivity of the photonic crystal, the magnitude of the acceleration can be calculated. It is shown that this structure can measure less than 0.4 mgn when the transmissivity intensity changes one out of 1 and its measuring range is up to 3.2 gn.