岩石II型断裂韧度的大小在预测岩石复合断裂破坏中起着重要的作用，其测试方法必须考虑控制裂尖的拉应力，以使II型断裂先于I型断裂发生。通过对现有剪切盒断裂模型测试岩石II型断裂韧度方法的分析，发现其理论模型的裂尖仍存在较大的拉应力，同时指出了该试验方法的不足，并提出了其改进测试的新方法，该方法更加符合方块试样的受力特性且更适合岩石II型断裂韧度测试。此外，利用有限元软件ABAQUS建模，并且修正了新剪切试验方法的II型断裂韧度计算公式，大大降低了其裂纹尺寸效应的影响。最后通过开展室内II型断裂韧度测试试验，获得了砂岩的II型断裂韧度，其均值约为3.09MPa?m0.5。该测试研究对于锦屏水电站工程实践提供一定的参考与应用价值。

The mode II fracture toughness of rock plays an important role in predicting composite fracture failure, and its test method should consider weakening the tensile stress at the crack tip, so that the mode II fracture occurs the first. Based on the shear-box method measuring mode-II fracture toughness from sandstone in Jinping Hydropower Station, it is found that large tensile stress still exists at the crack tip in theoretical model, and that the shortcomings of the original test method are pointed out. The experimental results show that the original shear-box mode is difficult to achieve pure shearing, which influences the results of the mode II fracture toughness. A new test method is proposed, which is symmetrically loaded and more fit for the mechanical characteristics of the shear-box with 45? and is more appropriate for mode II fracture toughness test of rock. In addition, the mode II fracture toughness formula of the new shear test methods is amended using the finite element software ABAQUS, which greatly reduces the impact of the crack size effect. Finally, by conducting mode II fracture toughness test trials, the mode II fracture toughness of sandstone is obtained, and the mean value is about 3.1MPa ? m0.5, which is greater than KIIC (2.65 MPa?m0.5) measured from the original shear-box. Some reference and application value would be provided by this test research for the engineering practice of Jinping hydropower station.