Against the background of the Inner-Mongolia 110 national highway reconstruction project and with the three-dimensional model of transition section and seven DOFs vehicle model is established, the influence of slabs on the pavement roughness is comprehensively analyzed when types of damages are done to the pavement, such as wavy irregularity and uneven settlement where left and right wheels go through, by taking car vertical acceleration, the wheel dynamic loading coefficient, and the front-rear wheel′s vertical displacement difference as the evaluation criteria. The results are as follows: without any slabs, the maximum vertical acceleration increases from 0.96 m/s2 to 3.78 m/s2 with the road grade reducing from A to C, and the maximum vertical displacement difference between front and rear wheels increases from 20.5 mm to 114.8mm. While with slabs, the maximum vertical acceleration increases from 0.87 m/s2 to 2.93 m/s2 , and the maximum vertical displacement difference between front and rear wheels increases from 18.7 mm to 34.2 mm, which indicates that the slabs intend to make the front wheel dynamic load coefficient reduce to a lower level the same as that on the higher grade road. But under the condition of uneven settlement road where left and right wheels go through, with the slab′s thickness increasing from 0 cm to 30 cm, the maximum vertical acceleration of car body reduces from 1.92 m/s2 to 1.13 m/s 2. When the slab′s thickness increases from 30 cm to 45 cm, the acceleration only reduces from 1.13 m/s2 to 1.03 m/s2, which is within the scope of uncomfortable standard of human body. Therefore, When the pavement where left and right wheels go through suffers from uneven settlement, the slabs have no significant effects on improving the vehicle smoothness, which requires other remedial measures.