The paper describes the system design for a nonideal capacitive micromichined accelerometer in MATLAB/SIMULINK. In this paper, a fourth-order sigma-delta micromachined accelerometer system design is represented, which includes the electrode movement and circuit noise. By simulation and comparison with the ideal 4th-order sigma-delta accelerometer in MATLAB, we have found that the SNR is essentially influenced by the electrode movement. Moreover the influence of the electrode stiffness Ke is researched. We have also researched the effects of the kT/C noise and the front-end amplifier noise. This nonideal accelerometer system can represent more accurate simulation result.