Abstract: A static analysis model for micro-machined switch consisting of a clamped-clamped beam is presented. In this model, the deflection of the clamped-clamped beam subject to the electrostatic force are divides into three stages:the first is a clamped-clamped beam subject to the electrostatic force without any constrain at the center;the second is a beam subject to the electrostatic force with a constraint at the center,i.e. the beam is subject to an extra reacting force at the center besides the electrostatic force;the third is a beam subject to both the electrostatic force and a reacting force with given deflection and angle of rotation over the central part of the beam. The reacting force at the second stage and the reacting force and its position at the third stage are related with the applied voltage. In the examples, a method to solve for the unknown boundary conditions and the applied voltage is presented and some results are given,including the relationship between the deflection at the center of the beam and the applied voltage,the effect of the length of the beam on the pull-in voltage,and the effect of the length of the electrode on the pull-in voltage,and so on,form which some beneficial conclusions can be obtained.