Three-dimensional（ 3 D） model for micro-mechanical structure（ MMS） of micro-electro-mechanical system（ MEMS） acceleration sensor ADXL 203 is set up. Castigliano Theorem and linear elasticity theory are used to derive the stiffness of folding beams in X

Y

and Z directions. And the stiffness calculation results are verified by ANSYS. Then the damping coefficients of MMS are solved. Finally

based on the damped forced vibration model

the response rule of MMS under shock pulse is analyzed by quasi-static theory or vibration theory. And the motion equation of MMS under the condition of half sine wave shock is derived. The maximum displacement of the structure in X and Y directions is 0. 883 mm and 0. 8786 mm

respectively. 0. 883 mm occurs at 0. 141 ms and 0. 8786 mm occurs at 0. 142 ms after shock. A solving method of stiffness

damping and motion equations of MMS is proposed

which is convenient for analyzing on failure mechanism and guiding the shock test of MEMS.