Abstract: In order to compare with the theoretical predicted results and the experiment results between the conventional max circumferential stress criterion and the corrected max circumferential stress criterion with the consideration of the T stress, the accuracy of the corrected max circumferential stress crack extension criterion established was verified. The T stress affected to the fracture toughness and the crack extension law was obtained. The three point bending half disc specimen was applied to study on the Type Ⅰ-Ⅱ complex fracture toughness and the crack initial extension angle with the change of the pre-cracking orientation. The study results showed that when the T stress was considered, the pure I type cracking extension angle would not be kept as 0 and the cracking extension orientation would be deflection. As for the Type Ⅰ-Ⅱ complex fracture, when the T stress was positive, the anti-cracking continuous extension capacity of the material would be enhanced and the fracture strength would be increased. When the T stress was negative, the anti cracking continuous extension capacity of the material would be weakened and the fracture toughness would be reduced. The T stress affected to the crack fracturing angle and the critical stress strength factor could not be ignored and especially would have obvious influence to the Type Ⅱ fracture. The GMTS criterion could be better to predict the compound crack initial extension angle and the fracture toughness of the rock.