Abstract: In order to study the influence of the seam between type Ⅰ slab ends and CA mortar on dynamic characteristics of rail, slab, and vehicle under high-speed train load, a vehicle-type Ⅰ slab track vertical coupling dynamic model was established. Through this model, the changes of evaluation indexes such as wheel-rail force, displacement of rail and slab, acceleration of rail, tensile stress of slab, acceleration of slab, and acceleration of vehicle were investigated under various working conditions for different seam lengths and heights at slab ends. The result indicates that with a shorter seam at the slab end, the track slab is easier to bear the force with a void. When the track slab bears the force with a void and a seam length, the seam height equals to the maximum vertical displacement of the track slab with the seam length. The force of track structure and vehicle is influenced by both the seam length and height, but more influenced by seam length. When the seam is less than 0.6 m long, the deformation and stress were deteriorated mainly on the rail and slab. When the seam is longer than 0.6 m, the vibration acceleration of vehicle will exceed the allowable value.