The present invention discloses a monolithic z-axis torsional CMOS MEMS accelerometer, it includes a matching frame, two anchors, a first comb structure, a second comb structure and a proof mass. With the implementation of the present invention, the capacitance sensitivity of Z+ direction and Z− direction sensing signals by the accelerometer can be improved. On the other hand, due to the feasibility of applying micromachining etch processes from the top side, the ease and the yield of production are both promoted.