The error principle caused by structural process imperfection of silicon micromechanical z-axis gyroscope in open mode is introduced firstly.  A new closed-loop control detection strategy is presented,  which would has advantage of minimizing the initial capacitance difference and restraining the cross-talk coupling errors.  The negative electrostatic spring effect of feedback force generator is analyzed in focus,  and its linear mathematics module is calculated out.  By computing the relation between the resonant frequency and feedback force added on the sense mode of MEMS z-axis gyroscope,  the inner relation between the ne gative electrostatic spring coefficient in sense axis and the voltage on the feedback force generator is deduced indirectly.  The theory has been testified by experiment,  which will lay foundation for the next design of closed-loop scheme.