Abstract: In order to evaluate the safety and comfort of trains for high-speed multiline railway bridges, it is necessary to perform a simulation research on coupled vibrations for multiline railway vehicle-bridges. For this study, the three-dimensional space dynamic models of CRH3 motor car and trailer were set up using a multibody system dynamics software SIMPACK, and the train dynamics model was assembled via the established CRH3 motor and trailer model by the substructure technology of SIMPACK. The dynamic analytical model of bridge was established by using finite element software ANSYS, for calculating the natural characteristics. Then, according to the deformation compatibility condition and force balance condition between the train system and bridge system, the data transfer of the displacement and force on the wheel-rail contact surface was conducted. The simulation study of multiline vehicle-bridge coupled vibrations was carried out by co-simulation based on SIMPACK and ANSYS for the first time. Meanwhile, the dynamic indexes of the bridge, comfort indexes, and safety indexes of the train were analysed to explore the general rules and influences of coupled vibrations on multiline vehicle-bridges. The research results are as follows:(1) The corresponding vehicle safety indexes (derailment coefficient, wheel unloading ratio, and wheel/rail lateral force) under the combined action of three line trains are almost the same as those only under single line action. As for the vehicle comfort indexes (vertical body acceleration, lateral body acceleration, vertical comfort index, and lateral comfort index), most of the corresponding indexes under single line and three line action are very close (within 1% difference), the only exception being individual vertical body acceleration with slightly larger difference (about 10%) between them. Hence, these comparisons show that the influence of bridge vibrations on the dynamic indexes of trains is small owing to the great stiffness of bridge structures. Thereby the values of corresponding dynamic indicators between single line condition and multiline condition are very close, i.e. the dynamic indexes of vehicles under multiline conditions can be speculated by those under single line conditions. (2) The midspan vertical displacement under the combined action of three lines is slightly larger than the algebra superposition displacement of single line, but less than 1%, and the influence coefficient of vertical displacement is between 1.001-1.006. The midspan lateral displacement under the combined action of three lines is close to the single line superposition displacement with about 10% difference, and the influence coefficient of vertical displacement is about 1.000. Therefore, the midspan vertical and lateral displacements under the multiline condition can be speculated by superposing all single lines. (3) The absolute value of midspan vertical acceleration under the action of three line trains is smaller than that of algebraic superposition for single lines with influence coefficients between 0.636-0.771; hence, it is feasible to conservatively evaluate the vertical acceleration of a bridge under multiline condition referring to the superposition of all single lines. The absolute value of midspan lateral acceleration under the action of three line trains is smaller than the maximum value among the absolute values of the lateral accelerations of each single line; thus, the lateral acceleration of a bridge under multiline condition can be evaluated referring to its single line lateral acceleration.