Abstract: At present, the experiments to study the frictional properties of rock fractures in the laboratory are conducted only under the stress state of normal stress and shear stress. However, the stress state in actual engineering is a true three-dimensional stress state. In other words, it is subjected to unequal normal stress, lateral stress, and shear stress in three directions simultaneously. Therefore, we conducted a double-shear rock fracture friction experiment under normal stress, lateral stress, and shear stress to study the frictional properties of rock fractures under true three-dimensional stress. The friction characteristics of rock fractures mainly include friction coefficient and friction coefficient drop. We analyzed the effects of lateral stress, shear rate, and shear displacement on the friction coefficient and friction coefficient drop of sandstone. The analysis shows that the friction coefficient increases with the increase of lateral stress and decreases with the increase of shear displacement. When the shear rate increases from 1 μm·s^-1 to 10 μm·s^-1, the friction coefficient decreases. When the shear rate increases from 10 μm·s^-1 to 100 μm·s^-1, the friction coefficient increases. The friction coefficient drop is independent of shear displacement and decreases with the increase of lateral stress. The friction coefficient drop is the largest at the shear rate of 10 μm·s^-1. This method designed the rock fracture friction experiment to be more consistent with the actual engineering stress state. Therefore, the experimental results obtained are more instructive for understanding the frictional properties of fractures in actual projects.