the proof mass 50 is subjected to forces not uniformly distributed because the weights at the two ends of the axis 51 are unequal as a result the proof mass 50 rotates about the axis 51 and drives the mobile single unit 62 on the second comb structure 40 to rotate and in consequence the capacitance of the first upper capacitor first lower capacitor second upper capacitor and second lower capacitor between the mobile single unit 62 and the first fixed single unit 61 or the second fixed single unit 63 varies when coupled given the variations in capacitance the magnitude of sensed forces applied along z axis can be calculated with the calculated magnitude of the forces applied along z axis it is feasible to estimate or calculate the acceleration along z axis so as for the accelerometer to function well referring to fig7 there is shown a schematic view of the operation of the monolithic z axis torsional cmos mems accelerometer 100 according to the embodiment of the present invention as shown in fig7 the proof mass 50 rotates about the axis 51 because the monolithic z axis torsional cmos mems accelerometer 100 moves in z axis direction referring to fig7 both the proof mass 50 and the second comb structure.