To improve the roborant capacity and the resolution of a micromechanical accelerometer, the nonlinearity of the system was studied. The mathematic model of the system was discussed and the variable electrostatic stiffness brought by the nonlinearity of a electrostatic torque was analyzed. Analytical results show that the preload voltage is used to be less than 0.707 time of crippling load voltage so as to make total stiffness greater than zero, which will cause a poor resolution when the input is near 0g. In view of the nonlinear effect, an adaptive adjustment method in which the total stiffness was kept a constant and the preload voltage and the feedback voltage were renewed every sampling cycle was proposed to improve the stability and resolution of the system. Finally, a digital micro accelerometer based on DSP was developed,then it was tested by using the adaptive adjustment method. Experimental results indicate that the resolution of the accelerameter is improved from 43.2 μg to 11.3 μg near 0g and from 36.4 μg to 12.1 μg near 1g. These data prove the system performance has been improved greatly.