In the case of the consideration of the nonlinear stiffness and damping of couplers and buffers,friction force between wheel and rail,the nonlinear dynamic impacting model of metro vehicle group is established.The nonlinear stiffness and damping of the buffer are determined by means of test.Simulation results of impacting characteristics between one vehicle and fixed body are verified by testing data.By numeric simulation,the impacting characteristics of two different metro vehicle groups are researched,in which there are 6 or 2 vehicles in every sub-group.It is found that when coupling impact between two vehicle groups takes place,impacting force,stroke of buffer between impacting interface of two group is maximum.When number of vehicles in sub-group is different,the maximum impacting force is not only different,but the stroke and energy dissipation of buffer is also different.In the couplers far from impacting interface between two groups,smaller capacity buffers could be used.