Abstract: In order to study the effect of cracks on the mechanics of ballastless track, a spatial finite element model of ballastless track with a crack was established based on the cracking characteristics of in-situ concrete layer, in which the singularity of the crack tip was simulated by 20-node hexahedron isoparametric singular element using the theory of elastic fracture mechanics. The mechanics of ballastless track under train load was then analyzed. The results show that the effect of the roadbed slab crack on the vertical displacements of rail and roadbed slab is small, and on the stresses of the top bar and concrete of the roadbed slab is not remarkable. Besides, the stress of the bottom bar has a sudden increase at the crack tip; the static and dynamic crack widths are almost the same. Under train load，for the roadbed slab with a 60 mm deep bottom crack, the crack width increases to 0.017 mm, and the bar stress at the crack tip is two times that without cracks.