Objective To explore the effects of the interfacial debonding caused by water environment in the mouth and the interfacial defects between the crown and cement on stress distributions in all-ceramic crowns. Methods The three-dimensional solid model of lithium disilicate CAD/CAM crowns for the first mandibular molar was established. Seven debonding states between inferior surface of the crown and top surface of the cement (Stage 1-7) as well as two interfacial defects (Case I and II) were defined in finite element software ABAQUS. The bottom of nine models was completely constrained. For stress calculation, the 600 N vertical load was applied at occlusal surface via an analytical rigid hemisphere with the diameter of 5 mm. Results Under occlusal vertical load, the stress on interior of the crown and top surface of the cement was mainly distributed at the boundary of the debonding areas and margin of the defects. The first principle stress on interior of the crown did not exceed its ultimate tensile strength, but the maximum tensile stress of the cement exceeded its ultimate tensile strength, leading to cohesive failure in the cement. Conclusions The axial wall played a critical role in maintaining the principal tensile stress of the crown at a lower level. The defects at bonding interface between the crown and cement had a more significantly impact on load capacity of the crown than the increase in debonding areas. In order to improve load bearing capacities of all-ceramic crowns, attention should be paid to avoid defects in clinical prosthodontic practices.