Abstract: The reliability of MEMS is a key problem for its commercial application.Fracture is a important factor for the failure.In this paper,we mainly focus on fracture Reliability for poly-silicon micro-cantilevers under shock load,expatiate on the failure mechanism of Fracture,and build a model using stress-strength principle.A lot of data will be collected after the shock experiment.Then the comparison between the experimental curve and the theoretic curve would be presented.