In order to investigate the vibration response characteristics and evaluate the stability and comfort of the straddle type monorail vehicle within the designed speed, the topology relationships among the traveling wheels, guide wheels, stabilizing wheels and bogie central traction devices are analyzed. A monorail vehicle spatial coupling dynamic model, which consists of three wheel-rail contact modes, is established based on Hamilton equation. The contacts to be studied are the one between the traveling wheel and the top surface of beam, and the contact of the side surface of the rail beam with the guide wheel and stabilizing wheel respectively. Several prominent characteristics such as the vibration dynamic responses of monorail lateral and vertical acceleration are obtained based on the coupling dynamic model when the roughness is designated to be the excitation source given the vechicle moving with a constant speed. Finally, the coupling dynamic model is validated with the comparison of the related experimental results. In this way, vibration response characteristics of monorail vehicle for different design speed are obtained under three rail surface roughness excitation. According to the simulated vibration results, the monorail vehicle stability and comfort performance through straight line is evaluated. The results infer that the monorail vehicle had outstanding comfort performance and excellent running stability.