Abstract: Based on the electrostatic force computation formulas of the rectangle capacitor with edge effects, a nonlinear static characteristic model of a torsion micro mirror is developed, and the effecting of edge effects on the static characteristics and on the pull in characteristics is also analyzed. By compared with experimental results, it is proved that the results by the presented model are closer to their practical counterparts. Numerical calculated results show that parameters, such as voltage, geometry dimensions of the micro mirror electrodes etc, can affect the edge effect, which leads a larger error in static response. Therefore, in some cases the edge effects must be considered when analyze the mechanical characteristics of micro mirrors.