This book firstly introduces the pertinent fundamental theory, important material and fabrication process of micro Gelectro mechanical systems. Based on these theories, the design rule and important engineering examples are described in detail. Then, many engineering applications for MEMS including the acceleration measurement, the angular speed measurement and the pressure measurement are introduced. Finally, finite element method is introduced in order to prove the correctness of the design.This engineering application of simulation includes the static and modal analysis of the beam, capacitance analysis, thermal G structure analysis of the device and fatigue analysis etc.