The present invention relates to a variable-area capacitor for a micromechanical sensor, a micromechanical comb grid capacitor accelerometer and a micromechanical comb grid capacitor gyroscope. Among them, the variable-area capacitor structure comprises of a movable and a fixed electrodes in each capacitor unit; a front surface of aforesaid movable electrode is parallel to that of aforesaid fixed electrode; the front surface of aforesaid movable electrode is in a rectangular shape, and the front surface of the fixed electrode is in a triangular or sawteeth shape or the front surface of the movable electrode is in a triangular or sawteeth shape, and the front surface of the fixed electrode is in a rectangular form; the triangular front surface is only overlapped with one long side of aforesaid rectangular front surface. Micromechanical sensors with variable-area capacitor structures of the invention can adjust elasticity coefficient as compared with present technology.