In this paper, the space model for train carriages is developed and introduced in dynamic analysis fo train-bridge interaction. The rail irregularities described by the power spectral deusity functions are generated by inverse Fourier transformation, The equations of motion of train-bridge systems are derived and reduced to simulate the dynamic responses of bridges under moving trains. The Newmark's + integration method is adopted to solve the non-linear coupling equations. Numerical examples show that the method of this paper has high accuracy in simulating trainbridge interactive dynamjes.