Abstract: Abstract: Traditional researches on vehicle rollover mainly focused on untrip rollover when vehicle running on the plat road, and 3DOF (three degree of freedom) model including lateral translational motion, yaw rotational motion and roll rotational motion was used widely. Obviously, the 3DOF model does not consider the influence caused by road excitation. But SUV (Sport Utility Vehicle) and commercial vehicle always run on the rough road, and the vehicle rollover characteristic were influence by the road condition impacts. For exploring the influence of road irregularity on vehicle dynamical rollover characteristic, a combined vehicle model was proposed. The model include six degree of freedom such as lateral translational motion, vertical translational motion, yaw rotational motion, roll rotational motion of vehicular body and two vertical translational motion of tires. The calculation program was built in MATLAB/ Simulink, and the vehicle rollover characteristic response parameters were calculated by Simulink with FISHHOOK test. The right road profile was a sine wave road coupling B grade road, the left road profile was B grade. Then a multi-body dynamical vehilcle model was built in Adams software. And the Adams vehicle model was used to calculate the results under the same work conditions with Simulink model, the results through Simulink model were compared with the values in the simulation test data of Adams model. Through comparison of simulation results, the Simulink model was proved correct. Secondly, the influences on roll angle caused by road grade, vehicle velocity and steering angle velocity were investigated. The results of simulation analysis showed that the simulation results of combined model were more accurate than the data of 3DOF and 4DOF model, the combined model results can consistent with Adams model result. The road irregularity, vehicle speed, steering wheel rotation speed have some effects on the vehicle roll characteristic, the roll angle during the steady state region increases as the rise of road grade, and the value during transient state has not obvious change. Vehicle roll angle increases as the rise of vehicle speed. And only the roll angle during the transient state is susceptible to rotation speed of steering wheel, which presented an augment with the increase of rotation speed. Further, the reason using simulation test on vehicle rollover characteristic research and the application of combined rollover model were discussed. Because of extremely dangerous and high economic cost, the majority research institution and automotive factory use the simulation test instead of on road test for vehicle rollover analysis, and commonly method is constructing multi-body dynamical simulaton model by Adams or LMS.Virtual.LAB/Motion. Then, simulation test was carried out based on the Fishhook and J-Turn test procedure. The application of combined rollover model was closely tied with vehicle control technology, such as differential braking, semi-active/active suspension, active steering, integrated chassis control and so on. These control method needs a state estimation to detect the impending vehicle rollover. Obviously, the accuracy of estimator is important to the control effect. The combined model has more accurate calculation result for vehicle roll angle and roll angle velocity than traditional 3DOF and 4DOF model.