To develop a four-degrees-of-freedom (DOF) dynamic model for B-double vehicles based on linear tire characteristics, a modeling method was proposed where the system was studied from a whole view. B-double vehicles were made of three vehicle units, including tractor, first semitrailer and second semitrailer. This method carried out the analysis on force and moment equilibrium of three vehicle units, moment equilibrium of second and third vehicle unit, and moment equilibrium of third vehicle unit, and then four differential equations were deduced and solved further. Compared with traditional method taking the analysis on force and moment equilibrium of each vehicle unit, respectively, six differential equations were then deduced. The advantages of whole method were that it did not need to overmuch substitute and solve the constraint conditions between vehicle unit, which decreased the tedious procedures during simplification and avoided the errors in calculations effectively. With the step angle input of tractor steering wheel, simulation results of these two methods are the same asthat of MATLAB, which verifies the validity of the whole method and lays the foundation for more complex dynamic model of multi-trailers combination vehicles in the next step.The results of physical parameter simulation for B-double vehicles were analyzed under low speed and high speed working conditions, respectively. It indicates that B-double vehicles possess rearward amplification (RWA) and are prone to instability more easily at high speed, which further verifies the validity of whole method.