Abstract: In order to solve the problems of low efficiency of numerical simulation of rail vehicle collision dynamic behavior and, the lack of crashworthiness analysis methods, a collision modeling and parameter optimization method is proposed for a carbody structure based on an equivalent stiffness method. According to the equivalent stiffness method and the equality principle of bending strain energy of a simply supported beam, the conditions for the equivalent bending stiffness of the hollow profile to a solid-core beam are put forward, the substitution formula of the equivalent parameters of the above two structures are deduced, and the equivalent parameters are optimized by the multi-island genetic optimization algorithm. The main vibration modal frequencies of the equivalent and the original model of the carbody structure are compared in detail, which proves the superiority of equivalent model reflecting the dynamic characteristics of original model, and the effectiveness of equivalent model of carbody structures. The change trend and error of numerical simulation results of the original and equivalent structures of an urban rail vehicle body are compared and analyzed, including the first-order vertical-bending and, the first-order torsional frequencies and, the main collision responses such as the speed, the acceleration, the energy and, the interface force of the carbody at a collision speed of 15 km/h. The research indicates that: the equivalent model of the hollow profiles can better reflect dynamic characteristics of the original model, in which the relative errors of the first-order vertical-bending and the first-order torsional frequencies of the carbody structure are 2.19% and 4.21%, respectively; the main occupant safety assessment index errors of the two models of carbodies are both less than 10%; and comparing with the original model, the element number is reduced by 38.91% and, the CPU calculating time is reduced by 27.63% in numerical simulation, which shows that the application of the carbody equivalent model in collision simulation can be feasible and effective.