Triaxial tests were conducted on composite model specimens (size:φ150mm×H450mm) and the effect of normal and along-slope loads caused by the gravity of the face slabs and the upstream water pressure on the extruded concrete curb (ECC) during operation period was simulated to study the influence of the confining pressure, slab thickness and water-binder ratio on the fracture mechanism and crack development of the ECC. The test results showed that the stress-strain curve went through three stages. During the first stage the voids between the components of “gypsum-slab-ECC-cushion material-gypsum” were compacted. The second stage was mainly about the compaction of the cushion material, whereas the third stage was mainly about the development of the cracks and the damage process of the ECC, during which the materials presented approximate linear-elastic characteristics. Initial cracks occurred in the overlap area between ECC rather than the tooth-shaped part connecting the cushion material. With the increase of the loads, the ECC was completely crushed then became a part of the cushion material. During the development of “initial crack-crack increase-final damage”, the damage rate of ECC increased from 15% to 50% and then to 100%, and the stress increased 1.5-2.0 MPa. The stress-strain of ECC was more sensitive to confining pressure and water-binder ratio than to the slab thickness.