The tire mechanics characteristics are essential for analysis, simulation and control of vehicle dynamics. This paper develops the UniTire model for tire forces and moments under combined slip conditions with anisotropic tire slip stiffness.The anisotropy of tire slip stiffness, which means the difference of tire longitudinal slip stiffness and cornering stiffness, will cause that the direction of tire resultant shear stress in adhesion region is different from that in sliding region. Eventually the tire forces and moments under combined slip conditions will be influenced obviously. The author has proposed a “direction factor” before to modify the direction of resultant force in the tire-road contact patch, which can describe tire forces at cornering/braking combination accurately. However, the aligning moments which are very complicated under combined slip conditions are not considered in previous analysis.The simplified physical tire model is introduced firstly in this paper to analyze the tire mechanics characteristics under combined cornering/braking situations, containing the tire forces and aligning moments. Then considering the influence of anisotropic tire slip stiffness and the expression of “direction factor”, a semi-physical tire model for tire forces and moments is given. Finally, the effectiveness of the model for tire forces and moments under combined slip conditions with anisotropic tire slip stiffness is validated by the comparison with the experimental data.