Abstract: Objective:This study aimed to evaluate the effect of the thickness and tooth preparation on fracture strength and failure mode of full-contour zirconia occlusal veneer. Methods：Standard artificial molars of 3 different groups(n=72) were prepared:Group A: the occlusal surface was ground of evenly by 0.5 mm; Group B: the occlusal surface was ground of evenly by 0.5 mm, and the axial surface was parceled for 1.5 mm; Group C: the occlusal surface was ground of evenly by 0.5 mm, and cavity fixation was prepared. Three different models of full contour zirconia occlusal veneers were designed with different thickness of 0.5 mm, 1.0 mm, and 1.5 mm respectively using CAD/CAM system and Dental Designer software. Fracture strength and failure mode of zirconia occlusal veneers were measured and recorded. Results：The average fracture strength value of full-contour zirconia occlusal veneer with different thicknesses and different preparation were: Group A:（1275.9±205.6）N（0.5 mm）,（2320.6±296.7）N（1.0 mm）,（4909.1±399.3）N（1.5 mm）；Group B:（1404.5±215.3）N（0.5 mm）,（2509.8±380.6）N（1.0 mm）,（4917.8±320.4）N（1.5 mm）；Group C:（1279.6±248.4）N（0.5 mm）,（2346.6±260.2）N（1.0 mm）,（4575.3±458.7）N（1.5 mm）. Fracture strength of full-contour zirconia occlusal veneers increased in parallel with the increase of their thickness. Fracture strength of occlusal veneers with different thickness and preparation was significantly different, while that of occlusal veneers with the same thickness but different preparation showed no significant difference. The failure mode of 0.5 mm group was similar to that of 1.0 mm group but different from that of 1.5 mm group. Conclusions：Thickness is a positive correlation factor for the fracture strength of full-contour zirconia occlusal veneers. Preparation has no effect on the fracture strength of occlusal veneers. 0.5 mm is an acceptable thickness for zirconia occlusal veneers in clinical practice.