The building, updating and application of the finite element model of high speed train car body are investigated. The complicated three dimension model of car body was represented by a simplified two dimension model, and reasonable coupled constraint conditions were imposed. First, the natural frequency and vibration modes of the car body were obtained by finite element modal analysis. Then the model was updated by using experiment results, parameters such as elastic modulus and density were modified. Finally, dynamic response of car body was calculated from the updated finite element model. The results indicates:1) The error of modified first four modes has been significantly reduced, the simulation coincides well with experiment data:2)The example of bolt failure simulation shows that the updated finite element model of car body can guide the placement strategy of testing point, analysis of testing results and fault judgment.