To investigate the dynamic effect of a moving vehicle on suspension bridge, this study suggests a finite element method. A method of establishing initial static equilibrium state of suspension bridge is proposed. Vehicle model has 6 degrees of freedom to idealize nonlinear multi-leaf suspensions and elastic tires of tractor-trailer. Irregular road surface of the bridge is generated using the road profile spectrum corresponding to actual road condition. Under the several vehicle speeds and weights, dynamic magnification factors of bridge responses are calculated.