Objective:To evaluate the effect of different shoulder width on the compressive strength of full-contour zirconia crowns.Methods:A computer aided design and computer aided manufacturing(CAD/CAM) system was used to prepare 24 full-contour zirconia crowns of the mandible first molar.1 mm occlusal thickness crowns with 4 shoulder width of knife-edge(group A),0.3 mm(group B),0.5 mm(group C) and 1.0 mm(group D) (n =6).The Co-Cr alloy PFM crowns made by the die of group C were used as the controls (n =6).All the full-contour zirconia crowns were bonded to the corresponding die using 3 M glass ionomer cement (GIC) and the compressive strength were measured by an universal testing machine.Based on the statistical analysis,crowns with the shoulder width of 0.5 mm were treated by the thermocycling test under cycling of 10000 times(group C1),20 000 times(group C2) and 30000 times (group C3) respectively(n =6).One-way ANOVA method was used for the statistical analysis.Results:The mean compressive strength(N) of group A,B,C,D and E was 3855.00 ± 305.47,2731.70 ± 261.80,3698.30 ± 276.87,3841.70 ± 544.88 and 2992.17 ± 168.41 respectively.The strength of group B and E were lower than that of group A,C and D(P ＜ 0.05),B vs E P ＞0.05.The compressive strength(N) of group C1,C2 and C3 was 3220.00 ± 504.38 (group C1),3148.33 ± 425.60(C2) and 2992.17 ±168.41 (C3) respectively (P＞0.05).Conclusion:For the full-contour zirconia crowns,both the knife-edge shoulder and the shoulder wider than 0.3 mm can meet the thermoclinical needs.The cycling times used in this study have no influences on the compressive strength.