Concrete rupture of the face slabs of concrete face rockfill dams (CFRD) is a typical structure failure mode of CFRD, especially for high CFRD. With the observation of the engineering cases of face slab concrete rupture, the large-scale finite element numerical analysis with fine meshes was conducted to analysis the mechanism of slab rupture of CFRD. From the analysis, it could be concluded that the fundamental reason of the failure is the deformation of rockfill body behind concrete face slabs. The direct mechanism of concrete rupture is the local stress concentration of the slabs, which is driven by rockfill deformation. The displacement of dam crest along the direction of river flow and the displacement of dam crest along the direction of dam axis from one abutment to another could be the index for determine the extent of face slab stress concentration. Concrete rupture of face slab has close relationship with dam height, river valley shape, rockfill quality, compacted density of rockfill, etc. Strictly control the total deformation of dam body, especially the deformation after reservoir impoundment, is the most effective measure for avoiding concrete face slab rupture.