Corrosion grooves or corrosion cavity in the structure of micro gyroscope can be obtained by deep reactive ion etching technology. The etching error in the processing has an important influence on the natural frequency, output accuracy and stability of the micro gyroscope. A finite element model of comb micromechanical gyroscope was established by using finite element analysis software ANSYS. The influence of the micro beam over etching induced by the machining error on inherent frequencies of the driving mode and the sensitive mode was studied by finite element analysis, the influence on the bandwidth and sensitivity of micro gyroscope was also examined by analytical method. The results show that micro beam stiffness and inherent frequency of micro gyroscope increase with the increase of the over etching angle. When the maximum over etching angle is ±2°, the change rates of inherent frequencies for the driving mode and sensitive mode are more than 14%. Moreover, etching error can reduce the work mode of micro gyroscope and make the interferential mode occur between driving mode and sensitive mode. Meanwhile, the frequency of interferential mode and driving mode are nearly equal, which affects the output precision of micro gyroscope. In addition, bandwidth decreases with the increase of over etching angle. Sensitivity varies erratically with the change of over etching angle. When the etching angle is between 0° and 1.5°, the sensitivity of micro gyroscope is higher than that without etching error case.