The study of vehicle safety properties special in the characteristics of driving safety is a challenging task for vehicle industry. Since vehicle roll behavior with steering input act an important part of driving safety, how to accurately depict vehicle dynamics in real driving scenes are of great concern. However, previous researches seldom consider relation between road excitation and vehicle lateral response with steering input. To remedy this, comprehension analyses on vehicle roll behavior with steering input are present in this paper. Based on the power spectral density (PSD) definition of road roughness and its relationship, three dimensional (3-D) road surface model is firstly created for international standardization organization (ISO) level A , level C, and level E road excitation. Also, the relationship between road excitation on wheel and 3-D road profile is illustrated. Then, a 6 degree of freedom (6-DOF) model including vertical and lateral dynamics is proposed. By varying vehicle parameters, such as vehicle total mass, track width, height of center of gravity (C.G.) of sprung mass, and distance from front axle to rear axle, the functional relationships between road excitation and rollover index (RI) are illustrated. The simulations results show that, 1) the influence of the C.G. height due to vehicle mass transferring on RI is most sensitive under constant road excitation; 2) a positive relationship between road excitation level and RI can be found under unvarying vehicle parameters. Finally, the proposed calculation functions are validated in CARSIM® software. Compared to the results obtained from CARSIM®, the proposed model can provide satisfied result, and the height of C.G. due to vehicle mass transferring and road excitation level cannot be ignored whilst analyzing vehicle roll behaviors with steering input. The research achievements provide a theoretical result to improve rollover theory and have significant effects on practical applications.