The Pelvis-Thorax Side Air Bag (PTSAB) is a typical restraint countermeasure offered for protection of occupants in the vehicle during side impact tests. Currently, the dynamic performance of PTSAB for occupant injury assessment in side impact is limited to full-vehicle evaluation and sled testing, with limited capability in computer aided engineering (CAE). The widely used CAE method for PTSAB is a flat bag with uniform pressure. The flat PTSAB model with uniform pressure has limitations because of its inability to capture airbag deployment during gap closure which results in reduced accuracy while predicting occupant responses. Hence there is a need to develop CAE capability to enhance the accuracy of prediction of occupant responses to meet performance targets in regulatory and public domain side impact tests. This paper describes a new CAE methodology for assessment of PTSAB in side impact. This method was developed and validated to component and full-vehicle tests, and was successfully used to guide the design and development of PTSAB. The bag was folded using simulation folding developed by LSTC. A particle method (Computational Fluid Dynamics) in LS-DYNA® was used to deploy the PTSAB. The PTSAB model was correlated at a component level using linear impact test, and force-deflection plots of the CAE model were matched with that of the test. The PTSAB model was then implemented in a full vehicle simulation. The key factors that play a role in correlating the model and its ability to predict the test results are discussed in this paper.