Requirements of side curtain airbag have continued to increase. The revised SINCAP, FMVSS-226 ejection mitigation and small overlap of IIHS had added these requirements. To meet all the requirements, high inflator energy and complex cushion shape became necessary. Such situations increased possibility of cushion failure while deploying. Unfortunately, all the design verification tests are usually completed in a relatively latter stage of development and repetitive testing is needed to consider large dispersion of failure probability distribution. Therefore, verification and design improvement by numerical simulation in an early stage are desirable. A simulation method which can verify CAB deployment was developed in this study. The developed method has three distinct features. Firstly, nonlinear fabric materials and membrane finite elements are used to consider fracture of cushion fabric. Secondly, a pre-simulation procedure had been established. An initial state for an accurate analysis can be obtained through the procedure. And lastly, gas flow analysis is adopted. Because gas flow is a main cause in many failure cases, it should be adequately considered. Based on results of computational fluid dynamics and testing, an analysis method had been developed. Three types of failure causes were found. The first is stress concentration at an edge. The second is excessively compressed flow. And the last is a direct hit of gas jet concentrated at an inactive pattern. The developed method was found to be appropriate for analyzing and solving failure problems, though further studies are needed for predicting the third type failure accurately.